Mechano-chemical upcycling of pultruded composite waste for reuse in concrete mixture

ABSTRACT

Effectively managing waste from pultruded composite materials is a pressing concern within the composites industry, given their composition of thermosetting resins. Currently, much of this waste ends up in landfills or is incinerated, despite the considerable environmental repercussions. Thus, repurposing pultruded waste for construction purposes not only enhances environmental sustainability but also provides a dependable source of construction materials. In M30 grade concrete structures, composite structures such as pavement slabs can be engineered with superior split tensile strength compared to existing alternatives, while still meeting required compressive strength specifications outlined in the mix design, by substituting fine waste (FW) for fine aggregate (filler) at a rate of ≥ 2.5wt%.

Keywords:
Composite; Thermoset plastic waste; Glass fibre; Concrete; Recycling

1. INTRODUCTION

The composites industry has broadened its scope to produce a vast array of Fiber Reinforced Polymer (FRP) products, including strengthening strips, sheets, reinforcing bars, structural profiles, sandwich panels, molded planks, and piping. These FRP products offer several advantages over traditional materials like steel, such as reduced weight, increased mechanical strength, flexible manufacturing shapes, easier installation, and enhanced durability, even in harsh environments. FRPs utilize matrices made of thermosetting or thermoplastic resins, often improved with fillers and additives. The manufacturing processes for these resins vary based on their molecular structures. For instance, thermosetting resins such as vinyl ester, polyester, and epoxy undergo irreversible chemical reactions that create durable cross-links within their molecular chains. In contrast, thermoplastic resins like polyethylene, polyurethane, polypropylene, and polyvinyl chloride (PVC) experience minimal chemical changes during production and can revert to their original monomer states if contaminated.

Typically, FRP composite materials used in various industries contain fibers like glass, carbon, or aramid, either in continuous or discrete forms, embedded in a matrix of thermosetting resins. The fiber content in these composites generally ranges from 12% to 60% by volume, with inorganic fillers or extenders making up 0% to 20% by volume. In certain polymer composite types, such as bulk molding compounds (BMC), fillers like calcium carbonate, talc, or mica powders can account for up to 50% of the composite’s weight, closely matching the volume fraction for these materials. Managing waste from these non-reprocessable thermosetting FRPs poses a critical issue due to limited disposal solutions. Unlike thermoplastics, thermosetting FRPs present considerable recycling hurdles as they cannot be easily remelted. Nevertheless, thermosetting resins remain prevalent in FRPs due to their expedited production capabilities, facilitated by low viscosity, superior impregnation and adhesion to fibers, and enhanced mechanical performance [¹,²,³,⁴,⁵].

Typically, FRP pultruded production waste is discarded due to the relatively low cost of raw materials, barring exceptions like aramid and carbon fibers. Although waste volumes generated are generally modest relative to product output, recycling may necessitate additional treatments such as heat curing prior to grinding. In new construction scenarios, minimal to no FRP off-cut waste is generated, as FRP components are custom-made and pre-molded to precise specifications. This differs markedly from traditional building materials like timber, which often require onsite cutting from standard sizes.

Deconstruction operations account for the majority of FRP waste, with production waste (mostly from trimming dust, defective goods, and trial runs) and building site garbage (usually from off-cuts) making up the remaining portions. Currently, the volumes of trash resulting from FRP deconstruction are insignificant when compared to other waste categories and are usually disposed of in landfills. But in the ensuing ten years, as FRPs are used more widely in more industries, it is expected that the amount of FRP waste generated after application will increase as well.

1.1. The drawback with FRP composite waste is not biodegradable

Fiber Reinforced Polymers (FRPs), as a specialized category of plastics, encounter many of the same issues as other plastics when it comes to waste disposal and recycling. The complex structures of polymers and monomers in plastics often make it difficult to separate and revert them to their original states. This complexity limits the recycling potential, with only about 20% to 30% of plastics being effectively recycled.

FRPs, comprising both the fiber and matrix components, face similar environmental challenges. Safe disposal methods have primarily focused on two high-temperature approaches: one involves incinerating the binding agents to recover some material cost as heat while filtering out non-combustible elements; the other method uses cement kilns to burn the non-combustible materials, allowing the fibers to integrate into the resulting cement matrix. Moreover, the challenge of separating the fibers from the matrix and preserving them for reuse makes the recycling of FRPs particularly difficult. The intricate process of breaking down FRPs into their core components—fibers and matrix—and then further separating the matrix into reusable plastics, polymers, and monomers complicates efforts towards environmentally sustainable practices. Although FRPs and other plastics can offer cost and energy savings compared to traditional materials, enhancing the environmental profile of FRPs is crucial. Future advancements in eco-friendly matrices, such as bio-plastics and UV-degradable plastics, hold promise Fiber Reinforced Polymers (FRPs), as a specific class of plastics, encounter significant challenges regarding waste disposal and recycling, much like other plastics. The intricate configurations of polymers and monomers in plastics make it difficult to effectively separate and return them to their original forms, limiting the recycling potential to about 20% to 30%. FRPs, consisting of both fibers and resin matrices, mirror these environmental concerns. Addressing the safe disposal of FRPs has largely focused on two high-temperature methods. One approach involves incinerating the binding agents to recover some of the material’s value in the form of heat while filtering out non-combustible elements [⁶, ⁷]. The other approach entails using cement kilns to burn the non-combustible material, allowing the fibers to become part of the resulting cement product. The inherent difficulty in separating fibers from their resin matrix and preserving them for reuse further complicates the recycling process of FRPs. Breaking down FRPs into their constituent components—fibers and matrix—and subsequently separating the matrix into reusable plastics, polymers, and monomers, remains a significant challenge for sustainable design and recycling practices. Despite these challenges, FRPs and other plastics often provide cost and energy savings over traditional materials [⁸]. To enhance the environmental profile of FRPs, ongoing research and development are focused on creating more eco-friendly matrices. Innovations in bio-plastics and UV-degradable plastics are promising avenues that could improve the sustainability of FRPs in the future.

1.2. Reuse

Following the waste hierarchy, FRP waste management options are prioritized as waste minimization, reuse, recycling, incineration with energy recovery/composting, and finally, incineration without energy recovery/landfill. Another method under active exploration is reclamation, where the original constituent fiber and matrix materials are reclaimed for reuse. Although its applicability is still up for debate, reuse holds a key place in the hierarchy. Composite fiber reinforced polymer (FRP) components are made up of many components that work together to produce unique material qualities. The way that FRPs are used, their applications, and their attachment to existing structures must therefore be taken into account when planning for deconstruction and reuse at the end of an application’s life. To find possible ways to improve design for repurposing or recycling in the future, it is important to analyze the production process [⁹-¹⁰]. Avoiding embedded metal fasteners is one precaution to take because they might cause problems when separating before grinding. Surface deterioration of fascia panels and moldings may affect their reusability, even if UV stability and color fading have been largely addressed by FRP producers.

1.3. Recycling

Although thermosetting resins are generally not recyclable, three sets of technology have arisen for recycling thermoset composite materials:

1. Mechanical recycling techniques involve mechanical comminution to reduce scrap size, generating recyclates.

2. Thermal recycling methods convert waste into material and energy using heat-based processes. Methods for recovering fiber, burning in cement kilns, or straightforward material incineration are available options. A thorough rundown of these methods is available elsewhere else.

3. Chemical recycling techniques disintegrate the polymeric matrix of waste composites by dissolving it in chemical solutions such as acids, bases, or solvents.

GFRP pultruded composites demonstrate significant energy savings, requiring only a fraction of the energy needed to produce steel or aluminum. Current recycling technologies for glass fiber composites encompass mechanical, thermal, and chemical methods.

1.3.1. Mechanical recycling of GFRTCW

Through milling procedures, composite waste is divided into different-sized recyclates for commercial mechanical recycling, which commenced in the 1970s. Although mechanical recycling can take many forms, it always involves breaking down composite material and then using shredding, crushing, milling, or other comparable mechanical techniques to reduce particle size. Afterwards, sieves and cyclones can be used to separate the resultant scrap bits into fibrous (rich in fibers) and powdered (rich in resin). The most common method for recycling FRP thermoset polymeric fiber composite materials is mechanical recycling. Furthermore, certain types of FRP products can be produced by customizing recycling procedures. One of the biggest knowledge gaps in the field of mechanical recycling is the influence of operating parameters on process energy consumption and recycle quality [¹¹,¹²,¹³,¹⁴,¹⁵]. This understanding is critical for assessing recycles’ reusability in prospective cross-sector or closed-loop applications. Filler-sized and fiber-sized recycled particles are the two primary product types obtained from the mechanical recycling of FRPs. In the resin matrix of newly produced fiber-reinforced polymers, filler-size particles that are obtained by mechanical treatments or cutting can be employed. This kind of waste is currently used by some composite manufacturers; in bulk and sheet molding compounds (BMC and SMC), it frequently replaces calcium carbonate. For example, further processing of the shredded GFRP waste involved milling with a Retsch SM2000 laboratory Cutting Mill. This procedure produced two size grades of milled GFRP waste: fine (FW) and coarse (CW) pultrusion waste. The grinding chamber was equipped with bottom sieves of varying mesh sizes. These recycled goods are made by using a blend of fibrous and powdered particle materials with different amounts and lengths of glass fibers. Particle size distribution and the concentrations of organic and inorganic fractions are evaluated when characterizing GFRP recycles.

1.3.2. Thermal recycling of GFRTCW

Currently, GFRTCW, akin to incombustible material, undergoes incineration in a cement kiln, elevating temperatures to approximately 1400°C for cement production. The residue from this process comprises glass fibers, which integrate into the resulting cast material for diverse applications. However, the gaseous emissions discharged from the kiln pose a significant environmental hazard due to their high toxicity and potential for polluting the surrounding environment.

1.3.3. Chemical recycling of GFRTCW

Due to their high chemical resistance properties, GFRTCW are challenging to degrade. Finding an effective method to degrade and utilize this waste source is crucial. While GFRTCW may disperse in certain acids, further processing for dilution, recycling, and purification of the degraded chemicals for reuse and safe disposal presents difficulties. Moreover, concentrating on recycled chemicals may potentially lead to environmental pollution, necessitating careful consideration and management.

1.4. Utilization of recyclate for engineering applications

Mechanical recycling recyclables can be used in closed-loop systems or in a variety of industries. Examples of businesses that recycle their production waste in-house and repurpose it into valley gutter products are Filon Products and Hambleside Danelaw. Furthermore, research has demonstrated that replacing sand aggregate fillers in polymer-based mortar products with 4–8% by weight of recycled glass fiber can improve the mechanical strength of the product. Further market opportunities for mechanically recycled Glass Fiber Reinforced Polymer (GFRP) are urgently needed, notwithstanding these encouraging applications.

Research indicates that up to 10% loading levels result in an acceptable loss of mechanical properties. Another study suggests that incorporating 20% recycled filler doesn’t significantly impair performance compared to a reference composite, offering benefits in terms of reduced material weight and final cost. However, at higher loading levels, both mechanical properties and processing may be adversely affected due to lower matrix density and increased resin absorption by the recyclates.

1.4.1. Recyclate in concrete mixture

Thus far, there has been little investigation into the possible application of recycled Fiber Reinforced Polymers (FRPs) as aggregate in concrete [¹⁶]. Considering the need to decrease natural aggregate extraction and the amount of FRP waste that ends up in landfills, using recycled FRPs as a substitute for coarse aggregate makes sense. But this strategy has certain drawbacks as well.

Primarily, not all crushing and grinding tools are effective for processing FRPs. While crushing mills can reduce larger FRP pieces to sizes ranging between 50 and 100 mm, further refinement through knife mills can yield particles as small as 50 mm. Nonetheless, the elongated shape of many fibrous particles resulting from mechanical processing may render them unsuitable as coarse aggregate due to potential anisotropic behavior in concrete.

In the event that the elongated shape and fibrous character of recycled FRP particles hinder their application as coarse aggregates, filler-sized particles may nevertheless be viable. According to recent studies [¹⁷], there are significant improvements in concrete performance in terms of mechanical and durability indices when fine aggregate is substituted with GFRP waste powder at substitution rates of 5% and 15%.

Particles smaller than 63 mm are found in GFRPW, which is created during FRP cutting. Low levels of very fine particles (<63 mm) in concrete mixtures are known to improve workability and minimize water requirements in fresh concrete, even though their high specific surface area may require more water to be used. Additionally, it reduces porosity in hardened concrete and encourages a filler effect. Nevertheless, each mixture needs to be tested separately because the effect of fine particle content on concrete behavior differs.

To thoroughly examine the technological viability of incorporating filler-sized debris produced by cutting GFRP parts, such as pultruded profiles and molded gratings, into the concrete production process, an experimental program [¹⁸,¹⁹,²⁰] was developed.

1.4.2. Pultruded recyclate in concrete mixture

The researcher has emphasized the substantial potential of Glass Fiber Reinforced Polymer (GFRP) wastes that are mechanically recycled and come from the GFRP pultrusion industry as partial replacements for fine aggregates in polymer concrete (PC) materials and as reinforcement [²¹, ²²]. Resin concrete, or PC, substitutes an epoxy resin or a thermoset polymer, usually unsaturated polyester, for the traditional cement paste binder.When compared to conventional cement-based concretes, PC has a number of improved features, such as a high strength-to-weight ratio, a quick drying time, low permeability, better impact and damping behavior, and resistance to a variety of chemicals, weathering agents, and frost agents [²³,²⁴,²⁵,²⁶,²⁷,²⁸,²⁹,³⁰,³¹,³²,³³,³⁴]. Nevertheless, disadvantages have been identified, including increased expenses, vulnerability to creep and high temperatures, insufficient fire protection, and comparatively high coefficients of thermal expansion and shrinkage. However, PC materials are now superior in their ability to integrate recovered wastes, primarily because the resin matrix is impermeable [³⁵,³⁶,³⁷], which lessens the loss of natural resources. Promising results from earlier research on GFRP waste-incorporated PC composites point to the need for more investigation in this area.

Numerous results have been released regarding the study on the % substitution of fly ash in cement for concrete mixtures. 30% replacement rate led to decreased compressive strength, but replacement levels of 10% and 20% in M25 grade concrete showed good compressive strength for 28 days [³⁸]. Although strength decreases initially and then increases as fly ash percentage increases, a 25% replacement of cement with fly ash in M20 grade concrete has improved strength attributes [³⁹]. Likewise, a 28-day maximum compressive strength was demonstrated in an M-30 mix with a water-to-cement ratio of 0.43 when fly ash was substituted for cement up to 20% by weight [⁴⁰]. In light of the observed decrease in strength with higher levels of fly ash replacement, particularly at 30%, an attempt has been made to address this challenge by introducing Glass Fiber Reinforced Tire Crumb Waste (GFRTCW) into the M30 grade concrete mixture.

1.5. World production, consumption and recycling of glass fibre reinforced polymer

1.5.1. International scenario

Efficiently recycling accumulated GFRP waste is imperative to mitigate environmental impacts and meet growing demand. Transforming GFRP waste into a valuable resource is essential, despite the considerable challenges it poses to the fiber-based recycling industry’s future. Presently, conventional waste disposal practices in the global composites market predominantly involve landfilling or incinerating scrap and GFRP. However, with increasing awareness of climate change, global warming, and the imperative for sustainable and circular economies, waste disposal industries are shifting towards comprehensive fiber recovery methods. This transition is driven by extensive research efforts focused on recycling GFRP waste, highlighting the urgency and potential for innovative solutions in waste management.

1.5.2. Indian scenario and technological gap

The Indian composites industry has seen robust growth over the past five years, catering to diverse raw materials, components, and sectors. In 2018, the Indian composites market reached an estimated 3.4 lakh metric tonnes, marking a 6.3% increase from the previous year and the highest growth rate since 2015. This growth is propelled by expansions in mass transportation, electrical and electronics, infrastructure, and building and construction sectors. Per capita composites consumption rose to 0.3 kg in 2018 from 0.25 kg in 2012. Addressing the aforementioned challenges could be achieved through a mechanism that efficiently recycles and reuses a significant portion of construction waste, reintroducing it into construction processes to substitute naturally sourced materials. This necessitates a circular economy approach that transforms construction and demolition waste into a valuable resource. Such practices can contribute to reducing the energy intensity and environmental footprints of buildings and infrastructure.

1.6. Waste management of GFRTCW

The management of waste from pultruded composite materials poses a significant challenge for the composites industry due to the nature of thermosetting resins used in their production, which cannot be reprocessed or recycled. Consequently, a considerable amount of thermoset composite waste is currently disposed of through landfilling and incineration, despite the significant environmental consequences associated with these methods. Utilizing pultruded waste in construction applications presents a promising solution to enhance environmental sustainability and provide a dependable source of materials for construction purposes.

2. MATERIALS AND METHODS

2.1. Materials

2.1.1. Glass Fibre Reinforced Thermoset Composite Waste (GFRTCW)

The waste material from GFRP pultruded profiles, obtained from MeenaFibreglas Industries in Pondicherry, exhibits remarkable strength, comparable to mild steel, making it suitable for applications in corrosive environments like FRP grating (refer to Figure 1). The study’s use of GFRTCW (refer to Figures 2 and 3) results from the shredding of residual materials created at the production site (MeenaFibreglas Industries, Pondicherry) during the cutting and assembly procedures of pultruded profiles. These waste materials are cured at temperatures close to 240°C and are made up of thermoset unsaturated polyester resin, continuous E-glass fiber, and pigment.

Figure 1
Grating using GFRP composite.

Figure 2
Pulutured profile.

Figure 3
Coarse waste generated during pultrusion and manufacture during grating application.

The mechanical properties of these pultruded wastes surpass those of mild steel (see Table 1). However, due to their superior mechanical strength compared to mild steel, these wastes present challenges in grinding or pulverizing them into fine powder.

Table 1
Mechanical properties of GFRTCW.

MECHANICAL PROPERTIES	PULTRUDED FRP	MILD STEEL
Tensile strength (MPa)	382	340
Flexural strength (MPa)	468.3	380
Flexural modulus (MPa) Izod impact (kgm/cm) Specific gravity Safe working temperature (°C)	22489 2.15 1.9 130	196000 1.5 7.8 600

The waste material, namely slotted waste/GFRTCW Pultruded Coarse and Fine waste (CW & FW), is generated during slotting processes for applications such as grating (refer to Figure 4). Mechanical processing is employed to utilize the GFRTCW, involving cutting with a Wood Cutting Vertical Band Saw Machine followed by pulverizing using a vertical Turret Milling Machine. During the slotting of GFRP pultruded profiles, both fine waste (FW) and coarse waste (CW) are produced, which are then separated through sieving. In order to move forward with the recycling technique in this research, two interrelated difficulties need to be overcome. Finding the best recycling procedure for these resources is the first step; the next is figuring out appropriate uses for the recycled materials. To create a worldwide cost-effective waste management solution, both components are interconnected and require consideration of many economic considerations. The utilization of M30 grade concrete structures with ≥2.5wt% fine waste (FW) replacing fine aggregate (filler) can enhance the split tensile strength properties of composite structures such as pavement slabs and achieve the required compressive strength as per mix design at 28 days.

Figure 4
Fine Waste (FW) and Coarse Waste (CW) during slotting for applications.

In the first stage of mechanical recycling, the GFRTCW is chopped and ground into fine trash, which is subsequently mixed into M30 grade concrete mixtures in place of M-sand in pavement structures. Tests for chemical resistance, absorption of water, split tensile strength, and compression capacity are all part of this process. Additionally, a case study explores the utilization of fine waste as a replacement for cement in cement mortar. Moreover, an alternative approach investigates the use of acid-etched GFRTCW coarse waste in plain cement mortar over different time intervals.

2.1.2. Fiber reinforced concrete mixture

The M30 grade concrete mixture comprises Portland Pozzolana cement with 30% Fly ash (PPC), sourced from Maha Cement in Chennai, along with fine aggregate (M-sand), GFRTCW, coarse aggregate (natural aggregate), and water. In the cement mortar, Ordinary Portland Cement (OPC 53 grade) is utilized.

2.1.3. Acids and solvents

Different acids including HCl (hydrochloric acid), H2SO4 (sulfuric acid), HNO3 (nitric acid), and organic solvents such as THF (tetrahydrofuran), CHCl3 (chloroform), (CH3)2CO (acetone), ethyl acetate, and a mixture of acids were employed to assess the solubility properties of GFRTCW. All chemicals were obtained from Sd.fine Chemicals and used as received.

2.1.4. Natural soils

Samples of various natural soils, including red soil, red soil with manure, river sand, and clay soil, were gathered from our university campus. These samples were collected to evaluate the environmental impact of GFRTCW in soil.

2.2. Experimental methods

2.2.1. Microscope studies

GFRTCW optical microscopy was performed at a magnification of 40× utilizing a Euromex microscope equipped with a Ziess CMEX 5000 camera from Holland. Analysis using scanning electron microscopy (SEM) was done with a VEGA3 TESCAN. In order to reduce charge effects, the outside and inside surfaces of the concrete samples that were exposed to UV radiation and GFRTCW were placed onto SEM stubs and then coated with gold.

2.2.2. Energy dispersive x-ray analysis studies

EDAX, an x-ray technique, was conducted in the VEGA3 TESCAN instrument to analyze the elemental composition of both the exterior and interior UV-degraded GFRTCW samples.

2.2.3. Cutting of linear GFRTCW

The continuous linear GFRTCW is cut perpendicular to the fiber orientation using a cutting vertical band saw machine. It is essential to cut the linear waste into smaller pieces before pulverizing it using a turret milling machine.

2.2.4. Pulverization of GFRTCW–Coarse Waste

GFRTCW was ground by milling on a Turret Milling Machine. Several mechanical processes were explored for grinding GFRTCW–CW, including pedestal grinding, ball milling, etc. However, after experimentation, Turret milling was determined to be the most effective method for grinding/pulverizing GFRTCW into fine powder (FW) and fiber waste obtained from the CW, owing to its high mechanical strength. These wastes were pulverized linearly to the fiber orientation. Given that most pultruded profiles have a linear structure, turret milling emerged as a pivotal method for rapid, cost-effective, and efficient pulverization compared to other mechanical grinding processes.

2.2.5. Sieving of pulverized and slotted GFRTCW

Following pulverization, the pulverized GFRTCW–FW underwent sieving using a hand sieve to separate the fine powder from the fibrous waste, which was then utilized in cement mortar. Additionally, sieving of slotted GFRTCW was performed to separate the fine powder from the fibrous waste for utilization in concrete mixtures.

2.2.6. Thermogravimetric analysis (TGA)

A sample piece (about 10 mg) is heated in a crucible with a nitrogen flow at a rate of 5°C per minute from 50°C to 950°C. To find the amount or percentage of weight loss at any given temperature, weight loss profiles are then evaluated.

2.2.7. Contact angle studies

Contact angle measurements were conducted using a Kyowa interface instrument from Japan. Samples of GFRTCW and 2.5wt% GFRTCW concrete, with flat surfaces measuring 1 cm × 1 cm, were utilized for these measurements.

2.2.8. Utilization of pultruded GFRTCW in concrete mixture

The utilization of pultruded waste in construction applications offers significant environmental sustainability benefits and provides a dependable source of construction materials. According to literature surveys, the use of GFRTCW–Fine Waste (FW) yields better results than GFRTCW–Coarse Waste (CW) for engineering applications.

This study examined the impacts of substituting GFRP composite waste (FW) for fine aggregate in an M30 grade concrete mixture using mechano-chemical recycling of GFRTCW. To evaluate the pavement’s performance, a number of tests were carried out, including contact angle, absorption of water, chemical resistance, split tensile strength, and its compressive strength. Initially, CW was pulverized into FW, and the FW was proposed for use in M30 grade concrete for pavement structures like road slabs. This approach aims to enhance durability and utilize waste materials for cost-effective replacements in construction applications.

2.2.9. Slump test

Following the sieving process, the fine waste was incorporated into concrete. Subsequently, slump studies were conducted on both fresh concrete and fresh GFRTCW concrete using a Slump cone to assess the workability of the concrete.

2.2.10. Compression strength test

In order to test the compressive strength of concrete, cube specimens measuring 150 × 150 × 150 mm were cast using M30 grade concrete. The specimens were evaluated utilizing a Compressive Testing Machine (CTM 3000 kN) following 7, 14, and 28 days of cure. The specimen was subjected to the load until it failed, at which point the failure weight was noted. Three specimens were produced and tested for each test, with the average value being used to determine the outcome. Equation 1 was used to compute each specimen’s compressive strength by dividing the greatest compressive force by its cross-sectional area.

Additionally, compressive strength testing for Portland Pozzolana cement (PPC) with varying percentages of GFRTCW in cement mortar, as well as OPC with varied surface-etched GFRTCW–CW in cement mortar, was conducted. Specimens were cast in sizes of 50 × 50 × 50 mm and tested using a Compression Testing Machine (CTM 500 kN).

(1) $$\text{Compression strength =}\frac{\text{Ultimate compressive load (N)}}{{\text{Area of cross section (mm}}^{\text{2}}\text{)}}$$

2.1.11. Split tensile strength test

In accordance with IS 5816:1959, the split tensile strength test was carried out. After the specimens were removed and any remaining water and grit was wiped off, they were cured in water for 7, 14, and 28 days. To make sure that the two opposing faces aligned in the same axial plane, a central line was painted on them. The upper and lower plates were carefully positioned to be parallel to one another. Without causing any shock, the load was applied gradually and increased at a nominal rate of 1.2 N/(mm²/min) until failure.

Split tensile value obtained using Equation (2) below,

(2) $$\text{Splitting tensile strength =}\frac{\text{2p}}{\text{(}\pi \text{DL)}}$$

Where

P is compressive load on the cylinder in (kN)

D is its diameter

L is length of specimens in (mm)

2.2.12. Water absorption test

The ASTM C642-81 guidelines were followed when performing the water absorption test on GFRTCW concrete specimens. To make sure everything dried completely, the specimens were first baked at 105°C to 110°C for 24 hours. Following the specimens’ removal from the oven, their weights were determined using a weighing device and noted as the specimen’s dry weight. After that, the samples were submerged in fresh water to allow them to absorb moisture. The specimens were taken out of the water at predetermined intervals of one hour, surface dried with clean towels, and then weighed again. At each interval of time, the weights were recorded. Until reliable values were acquired, this process was repeated.

Water absorption% value obtained using Equation (3) below,

(3) $$\text{Percentage of water absorption =}\frac{(\text{w2}-\text{w1})*100}{(\text{w1})}$$

2.2.13. Durability test

An essential part of evaluating durability is the acid resistance test. Both conventional and GFRTCW concrete specimens were tested for this study. The following concentrated acids were used: nitric acid (HNO3), sulfuric acid (H2SO4), and hydrochloric acid (HCl). The original version of these acids was utilized; they were obtained from SD Fine Chemicals. A solution with a pH of roughly two was created by volumetrically preparing 5% diluted sulfuric acid (H2SO4) with other acids for the acid attack test. First, the cubes’ weights were noted, and then they were submerged in the diluted acid solution for a whole day. The cubes’ weight loss and remaining compressive strength were measured and examined after the immersion.

3. RESULTS AND DISCUSSION

3.1. Analysis for environmental impacts of GFRTCW

In the case study’s current context, a sizable amount of glass fiber reinforced thermoset composite waste (GFRTCW) gets disposed of in landfills, which has a negative impact on the environment and adds to costs. However, recycling offers a chance to turn expensive waste disposal into a profitable supply of reusable material as environmental concerns and a related emphasis on resource conservation gain in importance.

This research paper focuses on assessing the environmental impact of pultruded composite waste under different environmental conditions before incorporating it into concrete mixtures.

3.1.1. Analysis of UV radiated GFRTCW

The prevalent use of glass fiber reinforced thermoset composite in exterior applications subjects it to prolonged sunlight exposure, increasing the risk of ultraviolet (UV) radiation damage. UV radiation can degrade the resin within the composite exposed to sunlight, leading to the detachment of glass fibers from the composite structure. This degradation compromises the quality and functionality of the composite applications over time.

3.1.1.1. Scanning electron microscope (SEM) analysis

The SEM examination of UV-degraded GFRTCW revealed significant insights. In Figure 5, the sample exhibited glass fiber composite exposed to sunlight without resin, indicating resin degradation and inadequate adhesion of glass fibers. This condition poses the risk of carcinogenic glass fibers dispersing into the atmosphere. Figure 6 depicts the resin-degraded exterior surface of the UV-degraded sample, with a highly irregular surface indicative of direct sunlight exposure. Conversely, Figure 7 illustrates the interior surface of the UV-degraded sample with minimal resin degradation and uniform glass fibers. Figure 8 shows the resin-degraded interior surface, with fewer imperfections compared to resin exposed to direct sunlight. These findings indicate that GFRTCW undergoes degradation when exposed to sunlight, with UV radiation leading to the disintegration of glass fibers from the sample surface, posing environmental pollution risks and potential health hazards upon inhalation.

Figure 5
UV radiated GFRTCW–Exterior surface, scale bar: 50 µm.

Figure 6
UV radiated GFRTCW–Exterior surface, degraded UP resin, scale bar: 5 µm.

Figure 7
UV radiated GFRTCW–Interior surface, scale bar: 100 µm.

Figure 8
UV radiated GFRTCW–Interior surface, scale bar: 20 µm.

3.1.1.2. EDAX analysis

EDAX analysis was conducted on the UV-radiated interior and exterior surfaces of the GFRTCW sample, utilizing SEM images. Smart Quant results obtained from this analysis revealed crucial insights. In Figures 9 and 10, a comparative study of the results shows a significant decrease in carbon content on the exterior surface (5.2%) compared to the interior surface (10.2%). These findings support the degradation of the resin component of the composite upon UV exposure.

Figure 9
EDAX Smart Quant results of UV radiated GFRTCW–Exterior surface.

Figure 10
EDAX Smart Quant results of UV radiated GFRTCW–Interior surface.

3.1.2. Thermal degradation of pultruded GFRTCW

The thermal stability, which refers to the capacity to uphold a consistent chemical structure amidst fluctuating environmental conditions such as exposure to elevated temperatures, is a pivotal factor in material assessment.

3.1.2.1. Thermal analysis of GFRTCW using electric bunsen burner

The physical thermal analysis of GFRTCW was conducted using an electric bunsen burner in the laboratory, as illustrated in the Figure 11.

Figure 11
Shows the thermal analysis of GFRTCW.

The process involved several stages: (a) the GFRTCW sample (1.777g), (b) initiation of degradation, (c) emission of toxic gas from the waste, (d) color change to ash, (e) residue of glass fiber, and (f) final residue (0.767g). The results obtained from the thermal analysis indicate that the GFRTCW contains unsaturated polyester resin, which degrades within 15 minutes at 600 ºC. It was observed during the burning process that GFRTCW emits a significant amount of toxic gas. If GFRTCW were to be incinerated, it would heavily pollute the environment. Therefore, it is imperative to consider alternative methods such as pyrolysis or recycling the waste for engineering applications.

3.1.2.2. Thermogravimetric analysis (TGA)

TGA (Thermogravimetric Analysis) was conducted to assess the relationship between sample weight loss and temperature variation. Additionally, TGA can determine glass fiber and moisture contents, serving as a quality control measure for the manufacturing process.

Glass fiber reinforced thermoset composite waste’s (GFRTCW) thermal stability and degradation process are evaluated using thermogravimetric analysis (TGA). A crucible containing a 7.191 mg sample piece is heated under nitrogen flow from 50°C to 950°C at a rate of 5°C/min. The amount or percentage of weight lost at different temperatures is determined by looking at weight loss profiles. After a weight drop of 1.87g from the starting weight of 7.191 g, the examination shows that the sample residue weights 5.321 g. This indicates that GFRTCW is made up of 26.004% thermoset resin and 73.995% glass fiber, as shown in Figure 12. Furthermore, the sample displays degradation that takes place between roughly 350ºC and 500ºC.

Figure 12
TGA of GFRTCW, 5°C/min.

3.1.3. Soil burial test of GFRTCW

To assess the environmental impact of GFRTCW on wet soil, the waste was submerged in different soil samples for durations of 7 days and 32 days, as illustrated in the Figure 13.

Figure 13
Depicts the soil burial test of GFRTCW conducted over a 32-day period across different soil conditions. (a) Red soil, (b) clay soil, (c) red soil with manure, and (d) river sand.

The results from both the 7-day and 32-day tests indicate no degradation of the sample under soil burial conditions with moisture. Furthermore, there are no observable changes in color or size reduction. These findings suggest that the sample exhibits resistance to degradation in soil, indicating a minimal risk of environmental pollution.

3.1.4. GFRTCW in aqueous condition

The environmental impact assessment of GFRTCW was conducted under aqueous conditions to evaluate both water quality and the degradation of the waste in a liquid medium.

The experiment spanning 32 days revealed that GFRTCW is not subject to degradation in an aqueous medium, with no observed alteration in the pH value of the water. These findings collectively indicate a negative environmental impact of GFRTCW. Therefore, it is imperative to find ways to utilize the waste to ensure environmental sustainability and the test specimens is illustrated in the Figure 14.

Figure 14
GFRTCW in aqueous condition. (a) Distilled water, (b) GFRTCW in water after 32 days.

3.2. Analysis for mechanical recycling (Pulverization) of GFRTCW–CW using turret milling machine

The turret milling machine is employed for pulverizing GFRTCW, thanks to its capability to handle high strength and high silica content. Initially, the pultruded GFRTCW–CW is gathered and weighed, totaling 100.775 g, These waste materials are then secured in the turret milling machine, aligned parallel to the fiber orientation, as illustrated in Figure 15a. Following the pulverization process (Figure 15), the coarse waste is transformed into fine waste and fibrous waste. The fine recyclate derived from this process is utilized for various engineering applications.

Figure 15
Pulverization of GFRTCW CW to FW in Turret Milling Machine. (a) fixing of GFRTCW in milling parallel to fibre orientation, (b) initial grinding of GFRTCW, (c) final grinding of GFRTCW, (d) pulverized GFRTCW–Fine Waste and, (e) pulverized GFRTCW–CW.

The utilization of a Turret Milling Machine for the mechanical grinding of GFRTCW (pultruded section) is compared to other grinding, milling, and pulverizing machines in both qualitative and quantitative aspects and it is shown in the Figure 16.

Figure 16
Pulverized GFRTCW (CW to FW). (a) GFRTCW–Coarse Waste, (b) Pulverized GFRTCW (FW and CW) 3.2.1 Sieving of GFRTCW slotted waste and pulverized waste from grating application.

Firstly, slotted waste was gathered from the slotting machine. This waste was then sieved using a 10 mm sieve, followed by a subsequent sieving using a 4.75 mm sieve, as illustrated in Figure 17. The coarse waste retained in both the 10 mm and 4.75 mm sieves was subsequently forwarded to the milling process for further pulverization.

Figure 17
Sieving of slotted waste using 10 mm and 4.75 mm to obtain fine waste for recyclate.

The fine waste of GFRTCW (as depicted in Figure 18), which passed through the 4.75 mm sieve, was employed as recycled material to substitute the fine aggregate in the M30 grade concrete mixture.

Figure 18
GFRTCW–Fine Waste (FW).

1 kg of recycled material obtained from the slotted waste underwent further sieving to examine the particle size distribution of the recyclate, as depicted in Figure 19.

Figure 19
Sieving of GFRTCW–FW.

The Figure 19 shows (a) 1 kg of GFRTCW waste (b) 2.36 mm sieve (c) 1.18 mm sieve (d) 600 micron sieve (e) 300 micron sieve (f) 150 micron sieve (g) pan. The results from the sieve analysis indicate that a significant portion of GFRTCW–FW was retained at 2.36 mm. Additionally, the utilization of fine waste involves replacing Manufactured Sand in concrete mixture with particles smaller than 4.75 mm and ranging between 150 microns and 4.75 mm.

3.2.1. SEM analysis of GFRTCW–FW

SEM analysis was conducted on the sample of pulverized GFRTCW fine waste. The resulting image (Figure 20) revealed the morphology of glass fibres and unsaturated polyester resin present in the recycle. The sample, as depicted in Figure 21, exhibits the morphology of glass fibers and unsaturated polyester resin within the recyclate.

Figure 20
SEM image of GFRTCW, scale bar, 20 µm.

Figure 21
SEM image of GFRTCW, scale bar: 10 µm.

The results derived from the mechanical recycling process, involving the pulverization of GFRTCW into recyclate, demonstrate an efficient and cost-effective method. Subsequent sieve analysis of the recyclate indicates its suitability as a fine aggregate for concrete mixture. Moreover, SEM analysis of the recyclate reveals no observable change or degradation of the unsaturated polyester resin (UP resin) on the surface of the glass fibers during the pulverization process.

3.3. Analysis of pulverized GFRTCW fine waste for replacement of M-sand in concrete mixture

3.3.1. Mix design for utilization of GFRTCW–FW for replacement of fine aggregate in M30 grade concrete mixture

1. Requirements regarding ingredient proportioning in concrete

   • a)

     Grade Level: M 30

   • b)

     Cement Type: OPC 53 grade accordance with IS 12269 (part 2) 1991

   • c)

     The compressive strength characteristic needed in the field after 28 days: 30 Newtons per millimeter

   • d)

     Fly ash Type: Class F

   • e)

     The aggregate’s maximum nominal size is 20 mm

   • f)

     The coarse aggregate has an angular shape

   • g)

     320 kg/m³ of cement is the minimum required (IS 456:2000)

   • h)

     Maximum cement content (IS456:2000 cl:8.2.4.2) is 450 kg/m³

   • i)

     The maximum ratio of cement to water is 0.45 (IS 456:2000; IS 456:2000 cl:7.1)

   • j)

     Workability: 100 mm (slump)

   • k)

     Severe exposure situation (IS 456:2000)

   • l)

     Supervision Level: Good

2. Test information for materials:

   • a)

     Cement Used: IS 12269-confirming OPC 53 grade

   • b)

     Cement’s specific gravity is 3.15

   • c)

     Class F fly ash, verifying IS 3812 (part 2)

   • d)

     Specific gravity of fly ash: 2.2

   • e)

     Specific gravity of

     • i)

       Coarse Aggregate: 2.74

     • ii)

       Fine Aggregate (M-sand): 2.73

   • f)

     Water absorption

     • i)

       Coarse Aggregate: 0.5 percent

     • ii)

       Fine Aggregate: 1.0 percent

As per stipulations, the mix design as been carried out for M-30 grade of concrete as shown in Table 2.

Table 2
Design mix proportion of M30 grade conventional concrete.

DESCRIPTION	CEMENT (kg/m3)	FINE AGGREGATE (kg/m3)	COARSE AGGREGATE (kg/m3)
Quantity	438	795	975
Ratio	1	1.815	2.226

• Replacement of GFRTCW Waste for M-S and 2.5% of GFRP Waste.
  M-S = 795 × 0.975 = 775.125.
  GFRTCW 2.5wt% = 795 × 0.025 = 19.875.

3.3.2. Casting of cubes and cylinders for concrete

For the purpose of performing tests on compression strength, split tensile strength, and acid resistance (durability), nine cubes measuring 150 × 150 × 150 mm (Figure 22) and seven cylinders with dimensions of 50 mm in diameter and 100 mm in height (Figure 23) were cast. These experiments were conducted on M30 grade conventional concrete and concrete with 2.5wt% GFRTCW at intervals of 7, 14, and 28 days.

Figure 22
2.5wt% concrete cube (150 × 150 × 150 mm).

Figure 23
CTM (cylinder–50 mm dia 100 mm height).

3.3.3. Workability test

For both M30 grade conventional concrete and concrete containing 2.5wt% GFRTCW, the workability test—also referred to as the slump cone test—was carried out using a slump cone, as shown in Figure 24.

Figure 24
Slump cone test.

For conventional concrete with 0% GFRTCW and concrete with 2.5% GFRTCW, the slump measurements differ, with values of 110 mm and 82 mm, respectively and the results were shown in the Table 3.

Table 3
Workability test result of concrete.

S.No.	FIBRE CONTENT	SLUMP VALUE (mm)	REMARKS
1	M30 grade conventional concrete	110	Medium slump
2	2.5wt% GFRTCW concrete	82	Medium slump

3.3.4. Compressive strength test

The attainment and improvement of compressive strength in compliance with IS guidelines. As shown in Figure 25, the compressive strength of 2.5wt% GFRTCW concrete at 28 days was 32.567 MPa, while that of conventional concrete at the same age was 40.2 MPa. These findings show that GFRTCW concrete’s strength and longevity are on par with those of regular concrete.

Figure 25
Compressive strength test result.

Based on the theoretical value obtained for M30 grade, it stands at 19.941 MPa. According to the literature survey, concrete tends to fail in the presence of fly ash exceeding 20% in compression strength within 7 days. In alignment with this, during the experiment, both conventional concrete and 2.5wt% GFRTCW concrete failed within 7 days, with values of 18.2 MPa and 14 MPa, respectively. However, in adherence to IS standards, the strength gradually increases, reaching maximum compressive strength for concrete at 28 days.

3.3.5. Split tensile strength test

The splitting tensile strength results for 2.5wt% GFRTCW concrete at 7 days show an increase of 1.43 MPa compared to conventional concrete, which exhibits a strength increase of 1.705 MPa. Furthermore, at 28 days, the maximum strength achieved for 2.5wt% GFRTCW concrete demonstrates an increase of 3.055 MPa compared to conventional concrete’s increase of 2.61 MPa, as depicted in Figure 26. These findings indicate that the strength and durability of GFRTCW concrete surpass those of conventional concrete.

Figure 26
Split tensile strength test results.

3.3.6. Water absorption test

The results of the water absorption test indicate a decrease in the percentage of water absorption as the GFRTCW content in the concrete increases, as illustrated in Figure 27.

Figure 27
Water absorption test result.

3.3.7. Acid resistance test

Given the inherent chemical resistance of GFRTCW to substances such as Nitric acid and Hydrochloric acid, an investigation was conducted to assess the suitability of 2.5wt% GFRTCW concrete for chemical resistance. The M30 grade Conventional Concrete and 2.5wt% GFRTCW concrete specimens underwent durability testing by being submerged in different acids, such as sulfuric acid, nitric acid, and hydrochloric acid, for a duration of 24 hours (see Figure 28). Comparative examination in sulfuric acid, nitric acid, and hydrochloric acid solutions showed that neither conventional nor GFRTCW concrete lost weight. However, the GFRTCW concrete exhibited a marginal reduction in weight loss (−8.015 g) compared to its original weight when subjected to Hydrochloric acid. Consequently, the utilization of GFRTCW concrete is deemed suitable for acid resistance, particularly in Nitric acid and Sulfuric acid environments, provided proper surface coating is applied (refer to Figure 28).

Figure 28
Acid resistance test result.

3.3.8. Contact angle test

Contact angle tests were conducted on M30 grade conventional concrete and 2.5wt% GFRTCW concrete, with the results depicted in Figures 29 and 30. The findings indicate a contact angle of 26.1ºC for conventional concrete and 87.7ºC for GFRTCW concrete. Both types of concrete exhibit a hydrophilic surface nature. However, it’s noteworthy that GFRTCW concrete demonstrates significantly lower hydrophilicity compared to conventional concrete.

Figure 29
Contact angle of M30 grade concrete.

Figure 30
Contact angle of M30 grade GFRTCW 2.5wt% concrete.

The results indicate that the inclusion of 2.5wt% GFRTCW in concrete leads to reduced water absorption and enhances the overall durability of the concrete.

3.3.9. SEM analysis of GFRTCW concrete

The SEM images reveal that the GFRTCW concrete sample exhibits strong binding with the concrete mixture, indicating excellent cohesion, as illustrated in Figures 31 and 32.

Figure 31
SEM image of GFRTCW 2.5wt% concrete, scale bar 100 µm.

Figure 32
SEM image of GFRTCW 2.5wt% concrete, scale bar: 200 µm.

4. SUMMARY AND CONCLUSION

Transforming coarse glass fibre reinforced thermoset composite waste into fine particles through mechano-chemical recycling enables its incorporation into concrete and cement mixtures using a Turret Milling Machine. By replacing at least 2.5wt% of fine aggregate with this recycled waste, M30 grade concrete structures, such as pavement slabs, can exhibit superior split tensile strength compared to conventional counterparts, while still achieving desired compressive strength at 28 days according to mix design specifications. This study demonstrates an effective, cost-efficient, and sustainable approach to repurpose GFRTCW (Fine Waste & Coarse Waste), diverting it from landfills and mitigating its significant negative environmental impact.

5. ACKNOWLEDGMENTS

The authors express gratitude to Meena Fibers for providing materials and conducting testing. Additionally, the authors extend their appreciation to the Department of Chemistry at Anna University for their technical support and access to laboratory facilities.

6. References

• ^[1]
  CORREIA, J.R., “GFRP Pultruded Profiles in Civil Engineering: Hybrid Solutions, Bonded Connections and Fire Behavior”, M.Sc. Thesis, Technical University of Lisbon, Lisbon, 2008.
• ^[2]
  EL HAGGAR, S., EL HATOW, L., “Reinforcement of thermoplastic rejects in the production of manhole covers”, Journal of Cleaner Production, v. 17, n. 4, pp. 440–446, 2009. doi: http://doi.org/10.1016/j.jclepro.2008.07.007.
  » https://doi.org/10.1016/j.jclepro.2008.07.007
• ^[3]
  PICKERING, S.J., “Recycling technologies for thermoset composite materials current status”, Composites. Part A, Applied Science and Manufacturing, v. 37, n. 8, pp. 1206–1215, 2006. doi: http://doi.org/10.1016/j.compositesa.2005.05.030.
  » https://doi.org/10.1016/j.compositesa.2005.05.030
• ^[4]
  BANK, L.C., Composites for construction: structural design with FRP materials, Hoboken, NJ, USA, Wiley, 2006. doi: http://doi.org/10.1002/9780470121429.
  » https://doi.org/10.1002/9780470121429
• ^[5]
  CORREIA, J.R., “Pultrusion of advanced fibre-reinforced polymer (FRP) composites”, Woodhead Publishing Limited, v. 175, n. 20, pp. 207, 2013.
• ^[6]
  CONROY, A., HALLIWELL, S., REYNOLDS, T., “Composite recycling in the construction industry”, International Oil Spill Composites: Part A, v. 37, pp. 1215–1218, 2006.
• ^[7]
  CONROY, A., HALLIWELL, S., REYNOLDS, T., “Composite recycling in the construction industry”, Composites. Part A, Applied Science and Manufacturing, v. 37, n. 8, pp. 1216–1222, 2006. doi: http://doi.org/10.1016/j.compositesa.2005.05.031.
  » https://doi.org/10.1016/j.compositesa.2005.05.031
• ^[8]
  HOBBS, G., HALLIWELL, S., “Recycling of plastics and polymer composites”, In: Composites and Plastics in Construction Conference, Watford, UK, pp. 263–277, 1999.
• ^[9]
  HALLIWELL, S., Advanced polymer composites in construction: BRE information paper IP7/99, Garston, CRC Press, 1999.
• ^[10]
  PICKERING, S.J., “Recycling technologies for thermoset Composite materials current status‖”, Composites. Part A, Applied Science and Manufacturing, v. 37, n. 8, pp. 1206–1215, 2006. doi: http://doi.org/10.1016/j.compositesa.2005.05.030.
  » https://doi.org/10.1016/j.compositesa.2005.05.030
• ^[11]
  CORREIA, J.R., “Pultrusion of advanced fibre-reinforced polymer (FRP) composites”, Woodhead Publishing Limited, v. 175, n. 20, pp. 207, 2013.
• ^[12]
  KELLER, T., Use of fibre reinforced polymers in bridge construction: Structural Engineering Documents, Zürich, International Association for Bridge and Structural Engineering, 2003. doi: http://doi.org/10.2749/sed007.
  » https://doi.org/10.2749/sed007
• ^[13]
  SHUAIB, N.A., MATIVENGA, P.T., “Effect of process parameters on mechanical recycling of glass fibre thermoset composites”, In: 23rd CIRP Conference on Life Cycle Engineering, pp. 134, 2016. doi: http://doi.org/10.1016/j.procir.2016.03.206.
  » https://doi.org/10.1016/j.procir.2016.03.206
• ^[14]
  SHUAIB, N.A., MATIVENGA, P.T., “Effect of process parameters on mechanical recycling of glass fibre thermoset composites.”, Procedia CIRP, v. 48, pp. 134–139, 2016. doi: http://doi.org/10.1016/j.procir.2016.03.206.
  » https://doi.org/10.1016/j.procir.2016.03.206
• ^[15]
  RIBEIRO, M.C.S., MEIRA-CASTRO, A.C., SILVA, F.G., et al, “Re-use assessment of thermoset composite wastes as aggregate and filler replacement for concrete-polymer composite materials: a case study regarding GFRP pultrusion wastes.”, Resources, Conservation and Recycling, v. 104, pp. 417–426, 2015. doi: http://doi.org/10.1016/j.resconrec.2013.10.001.
  » https://doi.org/10.1016/j.resconrec.2013.10.001
• ^[16]
  CORREIA, J.R., MARQUES, A.M., PEREIRA, C.M.C., et al, “Fire reaction properties of concrete made with recycled rubber aggregate”, Fire and Materials, v. 36, n. 2, pp. 139–152, Mar. 2012. doi: http://doi.org/10.1002/fam.1094.
  » https://doi.org/10.1002/fam.1094
• ^[17]
  ASOKAN, P., OSMANI, M., PRICE, A.D., “Improvement of the mechanical properties of glass fibre reinforced plastic waste powder filled concrete”, Construction & Building Materials, v. 24, n. 4, pp. 448–460, 2010. doi: http://doi.org/10.1016/j.conbuildmat.2009.10.017.
  » https://doi.org/10.1016/j.conbuildmat.2009.10.017
• ^[18]
  COUTINHO, A.S., Production and Properties of Concrete, Lisboa, Portugal, National Laboratory of Civil Engineering, 1998. (In Portuguese).
• ^[19]
  GALLIAS, J.L., KARA-ALI, R., BIGAS, J.P., “The effect of fine mineral admixtures on water requirement of cement pastes”, Cement and Concrete Research, v. 30, n. 10, pp. 1543–1549, 2000. doi: http://doi.org/10.1016/S0008-8846(00)00380-X.
  » https://doi.org/10.1016/S0008-8846(00)00380-X
• ^[20]
  GALLIAS, J.L., KARA-ALI, R., BIGAS, J.P., “The effect of fine mineral admixtures on water requirement of cement pastes.”, Cement and Concrete Research, v. 30, n. 10, pp. 1543–1549, 2000. doi: http://doi.org/10.1016/S0008-8846(00)00380-X.
  » https://doi.org/10.1016/S0008-8846(00)00380-X
• ^[21]
  ALMEIDA, N., “Reusing Slurry from Ornamental Stone in Concrete Protection”, M.Sc. Thesis, Technical University of Lisbon, Lisbon, 2004. (In Portuguese).
• ^[22]
  CYR, M., LAWRENCE, P., RINGOT, E., “Efficiency of mineral admixtures in mortars: quantification of the physical and chemical affects of fine admixtures in relation with compressive strength”, Cement and Concrete Research, v. 36, n. 2, pp. 264–277, 2006. doi: http://doi.org/10.1016/j.cemconres.2005.07.001.
  » https://doi.org/10.1016/j.cemconres.2005.07.001
• ^[23]
  ALMEIDA, N., BRANCO, F., SANTOS, J.R., “Recycling of stone slurry in industrial activities: application to concrete mixtures”, Building and Environment, v. 42, n. 2, pp. 810–819, 2007. doi: http://doi.org/10.1016/j.buildenv.2005.09.018.
  » https://doi.org/10.1016/j.buildenv.2005.09.018
• ^[24]
  ALMEIDA, N., BRANCO, F., BRITO, J., et al, “High-performance concrete with recycled stone slurry”, Cement and Concrete Research, v. 37, n. 2, pp. 210–220, 2007. doi: http://doi.org/10.1016/j.cemconres.2006.11.003.
  » https://doi.org/10.1016/j.cemconres.2006.11.003
• ^[25]
  TITTARELLI, F., MORICONI, G., “Use of GRP industrial by-products in cement based composites”, Cement and Concrete Composites, v. 32, n. 3, pp. 219–225, 2010. doi: http://doi.org/10.1016/j.cemconcomp.2009.11.005.
  » https://doi.org/10.1016/j.cemconcomp.2009.11.005
• ^[26]
  RIBEIRO, M.C.S., MEIXEDO, J.P., FIÚZA, A., et al, “Mechanical behaviour analysis of polyester polymer mortars modified with recycled GFRP waste materials”, Proceedings ICECE, v. 2011, pp. 75365–75371, 2011.
• ^[27]
  FOWLER, D.W., “Polymer in concrete: a vision for the 21st century”, Cement and Concrete Composites, v. 21, n. 5-6, pp. 449–452, 1999. doi: http://doi.org/10.1016/S0958-9465(99)00032-3.
  » https://doi.org/10.1016/S0958-9465(99)00032-3
• ^[28]
  RIBEIRO, M.C.S., TAVARES, C.M.L., FERREIRA, A.J.M., “Chemical resistance of epoxy and polyester polymer concrete to acids and salts”, J PolymEng, v. 22, n. 1, pp. 27–44, 2002. doi: http://doi.org/10.1515/POLYENG.2002.22.1.27.
  » https://doi.org/10.1515/POLYENG.2002.22.1.27
• ^[29]
  RIBEIRO, M.C.S., NÓVOA, P.R., FERREIRA, A.J.M., et al, “Flexural performance of poly ester and epoxy polymer mortars under severe thermal conditions”, Cement and Concrete Composites, v. 26, n. 7, pp. 803–809, 2004. doi: http://doi.org/10.1016/S0958-9465(03)00162-8.
  » https://doi.org/10.1016/S0958-9465(03)00162-8
• ^[30]
  RIBEIRO, M.C.S., FERREIRA, A.J.M., MARQUES, A.T., “Natural and artificial weathering effects on long-term performance of polymer mortars”, Mechanics of Composite Materials, v. 45, pp. 515–526, 2009. doi: http://doi.org/10.1007/s11029-009-9104-7.
  » https://doi.org/10.1007/s11029-009-9104-7
• ^[31]
  MARÍN, C.G., SANTIAGO, M.O., FERNANDEZ, J.R., et al, “Fire tests on polyester polymer mortars”, J PolymEng, v. 23, pp. 353–368, 2003.
• ^[32]
  RIBEIRO, M.C.S., REIS, J.M.L., FERREIRA, A.J.M., et al, “Thermal expansion of epoxy and polyester polymer mortars plain polymer mortars and fibre reinforced polymer mortars”, Polymer Testing, v. 22, n. 8, pp. 849–857, 2003a. http://doi.org/10.1016/S0142-9418(03)00021-7.
  » https://doi.org/10.1016/S0142-9418(03)00021-7
• ^[33]
  SILVA, M.A.G., SILVA, Z.C.G., PETROGRAPHIC SIMÃO, J., “Petrographic and mechanical aspects of accelerated ageing of polymeric mortars”, Cement and Concrete Composites, v. 29, n. 2, pp. 146–156, 2007. doi: http://doi.org/10.1016/j.cemconcomp.2006.08.003.
  » https://doi.org/10.1016/j.cemconcomp.2006.08.003
• ^[34]
  TAVARES, C.M.L., RIBEIRO, M.C.S., FERREIRA, A.J.M., et al, “Creep behaviour of FRP-reinforced polymer concrete”, Composite Structures, v. 57, n. 1–4, pp. 47–51, 2002. doi: http://doi.org/10.1016/S0263-8223(02)00061-2.
  » https://doi.org/10.1016/S0263-8223(02)00061-2
• ^[35]
  BIGNOZZI, M.C., SACCANI, A., SANDROLINI, F., “New polymer mortars containing polymeric wastes, Part 1: Microstructure and mechanical properties”, Composites. Part A, Applied Science and Manufacturing, v. 31, n. 2, pp. 97–106, 2000. doi: http://doi.org/10.1016/S1359-835X(99)00063-9.
  » https://doi.org/10.1016/S1359-835X(99)00063-9
• ^[36]
  GARBACZ, A., SOKOLOWSKA, J.J., “Concrete-like polymer composites with fly ashes-comparative study”, Construction & Building Materials, v. 38, pp. 689–699, 2013. doi: http://doi.org/10.1016/j.conbuildmat.2012.08.052.
  » https://doi.org/10.1016/j.conbuildmat.2012.08.052
• ^[37]
  NÓVOA, P.J.R.O., RIBEIRO, M.C.S., FERREIRA, A.J.M., et al, “Mechanical characterization of lightweight polymer mortar modified with cork granulates”, Composites Science and Technology, v. 64, n. 13-14, pp. 2197–2205, 2004. doi: http://doi.org/10.1016/j.compscitech.2004.03.006.
  » https://doi.org/10.1016/j.compscitech.2004.03.006
• ^[38]
  GOUD, V., SONI, N., VARMA, G., et al, “Partial replacement of cement with fly ash in concrete and its effect”, IOSR Journal of Engineering, v. 6, n. 10, pp. 69–75, 2016.
• ^[39]
  KESHARWANI, K.C., BISWAS, A.K., CHAURASIYA, A., et al, “Experimental study on use of fly ash in concrete”, Int. Res. J. Eng. Technol, v. 4, n. 9, pp. 1527–1530, 2017.
• ^[40]
  CHOURE, A., CHANDAK, R., “Experimental study on concrete containing fly ash. International Research”, Journal of Engineering Technology, v. 4, n. 2, pp. 202–205, 2017.

Publication Dates

• Publication in this collection
  09 Sept 2024
• Date of issue
  2024

History

• Received
  14 June 2024
• Accepted
  03 July 2024