Influence of microstructural and morphological properties of raw natural clays on the reactivity of clay brick wastes in a cementitious blend matrix

Schackow, A.; Correia, S. L.; Effting, C.

doi:10.1590/0366-69132020663782852

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Articles • Cerâmica 66 (378) • Apr-Jun 2020 • https://doi.org/10.1590/0366-69132020663782852 copy

Influence of microstructural and morphological properties of raw natural clays on the reactivity of clay brick wastes in a cementitious blend matrix

Influência das propriedades microestruturais e morfológicas de argilas in natura na reatividade de resíduos de tijolos em uma matriz cimentícia

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The physical, chemical, and mineralogical characteristics of raw clays used in the industries interfere greatly in the production process and final ceramic product. Raw clays from 4 industries in the South of Brazil were characterized by the XRD, XRF, FTIR, DSC, and SEM techniques. In addition, the pozzolanic potential was also verified based on the kaolinite content of the raw samples. The raw clay that presented the highest pozzolanic potential had a quantity of kaolinite of 69.7%. The use of 40% of the brick waste produced with this raw clay (particle size of 75 μm) replacing Portland cement in a mortar resulted in a gain of 51% in compressive strength at 28 days. The analysis of the hydration products resulting from the Ca(OH)₂ reaction from the cement hydration with the ceramic waste showed the presence of Al₂O₃.2SiO₂ forming the C-S-H gel.

Keywords:
raw clay characterization; clay brick waste; clay microstructure; pozzolanic clay; cement hydration product

Table I Information about the industries that supplied the clayey masses.

Industry	A	B	C	D
Clayey ceramic mass composition	83% clay+17% other raw materials	85% clay+15% other raw materials	30% clay+70% other raw materials	50% clay+50% other raw materials
Annual production of bricks	7 million	1.4 million	2.16 million	3 million
Amount of discarded bricks	1-5% (6000 to 30000 pieces/month)	1% (1200 pieces/month)	5% (9000 pieces/month)	2% (6000 pieces/month)

Table II Mass of components used to prepare 1.75 L of mortars.

Mortar	Cement (g)	BW 75 μm (g)	Lime (g)	Sand (g)	Water (g)
Reference	157.6	-	163.6	1322.0	394.4
M40BW	86.7	57.8	190.7	1519.3	361.1

Table III Chemical composition (% by mass) of raw clays A, B, C, and D.

Oxide	A	B	C	D
SiO₂	58.53	49.76	47.14	59.67
Al₂O₃	22.54	27.52	26.42	20.34
Fe₂O₃	6.56	7.58	10.33	7.11
TiO₂	1.39	1.69	1.30	0.94
K₂O	0.77	0.88	0.56	3.59
CaO	0.20	0.18	0.17	0.09
MgO	0.54	0.34	0.40	1.03
Na₂O	0.21	0.10	0.11	0.13
P₂O₅	0.10	0.16	0.11	0.13
MnO	0.05	0.05	0.08	0.06
LOI*	9.10	11.74	13.39	6.56

Table IV Quantification of the phases (% by mass) present in raw clayey ceramic masses.

Clay	Kaolinite/halloysite	Quartz (impurity)	Hematite	Others*
A	57.1	32.0	6.5	4.4
B	69.7	17.3	7.6	5.4
C	66.9	16.1	10.3	6.7
D	51.5	35.7	7.1	5.7

Table V Properties of mortars.

Mortar	BW (%)	w/c ratio	Consistency index (mm)	Compressive strength, 28 days (MPa)	Compressive strength, 90 days (MPa)
Reference	0	2.50	267	2.5 ± 0.7	5.7 ± 0.4
M40%BW	40	2.50	190	6.4 ± 0.2	6.5 ± 0.8

Table VI Results of semi-quantitative chemical analysis by EDS of points 1, 2 and 3 indicated in Figs. 6 and 7.

Figure	Point	C	Na	MgO	Al₂O₃	SiO₂	K₂O	CaO
6	1	17.40	-	-	16.18	15.56	-	50.86
	2	12.58	1.13	3.15	12.24	17.45	3.58	49.87
	3	18.46	-	5.16	14.06	13.63	-	48.68
7	1	5.09	-	2.50	15.32	28.51	-	48.58
	2	6.09	-	4.63	14.83	28.68	-	45.78
	3	5.77	-	-	14.57	34.18	-	45.48

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[1] * adilson.schackow@udesc.br