Influence of concrete strength, fiber content and aspect ratio in the residual flexural strength of steel fiber reinforced self-compacting concrete

Cardoso, Matheus Galvão; Lameiras, Rodrigo de Melo; Capuzzo, Valdirene Maria Silva

doi:10.1590/S1983-41952021000500003

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ORIGINAL ARTICLE • Rev. IBRACON Estrut. Mater. 14 (5) • 2021 • https://doi.org/10.1590/S1983-41952021000500003 copy

Influence of concrete strength, fiber content and aspect ratio in the residual flexural strength of steel fiber reinforced self-compacting concrete

Influência da resistência à compressão do concreto, teor de fibra e fator de forma das fibras, na resistência residual do concreto autoadensável reforçado com fibra de aço

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) is a material that combines the benefits of self-compacting concrete in the fresh state and the greater durability, with the gains of fiber- reinforced concrete in the hardened state, especially the gains in residual flexural strength. Results are presented in this paper of residual flexural strengths on 48 prenotched prisms conducted in accordance with RILEM TC 162 TDF for the Steel Fiber Reinforced Self-Compacting Concretes (SFRSCC). This article presents equations to estimate residual flexural stresses in SFRSCC. For this, SFRSCC prisms of two compressive strength classes, 20 MPa and 40 MPa, were produced with 3 different types of steel fibers with the contents volume of 0.5% and 1.0%. Based on the test results, equations were proposed to determine the residual flexural stresses established through regression analysis, which were, then, further validated with concretes produced in this work and results available in the literature. The equations found, despite showing an indication of the residual flexural strengths that will be achieved, obtained a relatively high error. In order for the equations to be applied in a technical way, further studies for a larger sample need to be carried out, seeking to optimize the equations.

Keywords:
steel fiber reinforced self-compacting concrete (SFRSCC); flexural residual strength; three point bending test; hooked end fiber

Fiber Type	Diameter d_f (mm)	Length l_f (mm)	Aspect ratio l_f/d_f	Nominal Young’s modulus (MPa)	Nominal unit weight (Kg/m³)
ST-33/44	0.75	33	44	210	7850
ST-33/60	0.55	33	60	210	7850
ST-50/67	0.75	50	67	210	7850

Mixtures	20 MPa							40 MPa
Mixtures	REF	ST-33/60		ST-50/67		ST-33/44		REF	ST-33/60		ST-50/67		ST-33/44
Fiber Volume (%)	0.00	0.50	1.00	0.50	1.00	0.50	1.00	0.00	0.50	1.00	0.50	1.00	0.50	1.00
Coarse aggregate (G) (kg/m³)	852	844	826	834	802	826	804	852	844	805	834	806	826	803
Sand (S) (kg/m³)	633	627	614	619	596	613	597	633	649	600	641	599	635	597
Cement (C) (kg/m³)	378	382	392	388	398	392	393	498	505	515	513	515	519	520
Limestone Filler (kg/m³)	242	244	252	249	281	252	287	133	134	177	137	180	138	173
Superplasticizer (SP) (kg/m³)	3.90	5.00	5.20	4.10	4.00	5.20	5.50	5.10	5.30	6.10	6.50	6.10	6.60	5.20
Water (W) (kg/m³)	231	234	240	237	244	240	240	231	234	238	237	238	240	241

Concrete mix		f_fct,L [MPa]	f_ct (0.7*f_fct,L) [MPa]	Residual Flexural Strength
Concrete mix		f_fct,L [MPa]	f_ct (0.7*f_fct,L) [MPa]	f_R.1 [MPa]	f_R.2 [MPa]	f_R.3 [MPa]	f_R.4 [MPa]
20-05ST-50/67	Avg.	3.68	2.58	3.69	4.01	4.05	3.95
	CoV	4.4%	4.4%	20.1%	24.3%	24.0%	23.3%
20-1ST-50/67	Avg.	3.97	2.78	5.48	5.89	5.77	5.28
	CoV	14.8%	14.8%	18.9%	20.1%	18.2%	19.4%
20-05ST-33/60	Avg.	3.07	2.15	3.06	3.07	3.02	2.86
	CoV	16.9%	16.9%	8.5%	10.5%	10.8%	9.8%
20-1ST-33/60	Avg.	3.92	2.75	5.73	5.58	5.07	4.57
	CoV	10.4%	10.4%	4.4%	4.9%	5.7%	7.8%
20-05ST-33/44	Avg.	3.76	2.63	2.72	2.86	2.81	2.66
	CoV	8.1%	8.1%	12.6%	8.1%	6.6%	5.1%
20-1ST-33/44	Avg.	4.17	2.92	4.74	5.01	4.77	4.28
	CoV	6.6%	6.6%	10.3%	11.6%	8.6%	5.8%
40-05ST-50/67	Avg.	4.87	3.41	5.52	6.48	6.73	6.40
	CoV	3.9%	3.9%	9.6%	11.2%	10.8%	10.0%
40-1ST-50/67	Avg.	4.07	2.85	8.95	9.84	9.24	8.65
	CoV	37.7%	37.7%	2.9%	2.3%	6.3%	7.6%
40-05ST-33/60	Avg.	5.17	3.62	6.17	6.68	6.54	6.06
	CoV	2.4%	2.4%	9.0%	7.9%	4.7%	4.1%
40-1ST-33/60	Avg.	5.28	3.69	9.42	10.66	9.96	8.44
	CoV	10.7%	10.7%	1.6%	3.9%	5.2%	4.8%
40-05ST-33/44	Avg.	4.10	2.87	3.66	3.88	3.75	3.54
	CoV	6.1%	6.1%	5.6%	8.3%	7.8%	9.0%
40-1ST-33/44	Avg.	4.41	3.08	5.82	6.31	5.94	5.46
	CoV	6.2%	6.2%	3.6%	7.9%	12.5%	15.2%

Concrete Mix		Experimentally obtained vs. predicted by the equation
Concrete Mix		f_R.1 [MPa]	f_R.2 [MPa]	f_R.3 [MPa]	f_R.4 [MPa]	Error f_R.1	Error f_R.2	Error f_R.3	Error f_R.4
20-05ST-50/67	Exp.	3.69	4.01	4.05	3.95	1.13%	6.53%	6.75%	6.44%
20-05ST-50/67	Predicted	3.65	3.77	3.80	3.71	1.13%	6.53%	6.75%	6.44%
20-1ST-50/67	Exp.	5.48	5.89	5.77	5.28	13.04%	10.61%	6.85%	6.90%
20-1ST-50/67	Predicted	6.30	6.59	6.19	5.68	13.04%	10.61%	6.85%	6.90%
20-05ST-33/60	Exp.	3.06	3.07	3.02	2.86	11.21%	13.94%	15.64%	17.62%
20-05ST-33/60	Predicted	3.44	3.56	3.58	3.47	11.21%	13.94%	15.64%	17.62%
20-1ST-33/60	Exp.	5.73	5.58	5.07	4.57	6.02%	12.75%	15.03%	15.80%
20-1ST-33/60	Predicted	6.10	6.39	5.97	5.43	6.02%	12.75%	15.03%	15.80%
20-05ST-33/44	Exp.	2.52	2.75	2.74	2.63	26.66%	47.71%	45.95%	40.61%
20-05ST-33/44	Predicted	1.99	1.86	1.88	1.87	26.66%	47.71%	45.95%	40.61%
20-1ST-33/44	Exp.	4.74	5.01	4.77	4.28	2.05%	6.81%	11.55%	11.60%
20-1ST-33/44	Predicted	4.64	4.69	4.27	3.83	2.05%	6.81%	11.55%	11.60%
40-05ST-50/67	Exp.	5.52	6.48	6.73	6.40	11.29%	7.57%	2.59%	0.23%
40-05ST-50/67	Predicted	6.23	7.01	6.91	6.41	11.29%	7.57%	2.59%	0.23%
40-1ST-50/67	Exp.	8.95	9.84	9.24	8.65	0.74%	0.08%	0.61%	3.21%
40-1ST-50/67	Predicted	8.88	9.83	9.30	8.38	0.74%	0.08%	0.61%	3.21%
40-05ST-33/60	Exp.	6.17	6.68	6.54	6.06	5.81%	1.69%	1.24%	1.59%
40-05ST-33/60	Predicted	5.83	6.57	6.45	5.97	5.81%	1.69%	1.24%	1.59%
40-1ST-33/60	Exp.	9.42	10.66	9.96	8.44	8.27%	10.28%	9.38%	3.44%
40-1ST-33/60	Predicted	8.70	9.67	9.11	8.16	8.27%	10.28%	9.38%	3.44%
40-05ST-33/44	Exp.	3.66	3.88	3.75	3.54	8.37%	11.35%	12.63%	10.82%
40-05ST-33/44	Predicted	3.99	4.38	4.30	3.97	8.37%	11.35%	12.63%	10.82%
40-1ST-33/44	Exp.	5.82	6.31	5.94	5.46	9.17%	8.69%	7.26%	3.91%
40-1ST-33/44	Predicted	6.41	6.91	6.40	5.68	9.17%	8.69%	7.26%	3.91%

Concrete Mixture	$f_{c'}$ [MPa]	l [mm]	d [mm]	l/d	Fiber volume content (%)
M32	38.60	60	0.90	66.67	0.25
M34	37.30	60	0.90	66.67	0.50
M36	36.00	60	0.90	66.67	0.75
M38	41.10	60	0.90	66.67	1.00
M42	38.90	60	0.90	66.67	0.25
M44	39.70	60	0.90	66.67	0.50
M46	38.10	60	0.90	66.67	0.75
M48	39.70	60	0.90	66.67	1.00

Concrete Mix		Experimental data obtained by Venkateshwaran et al. (2018) vs. Values predicted by the proposed equations
Concrete Mix		f_R.1 [MPa]	Error f_R.1	f_R.2 [MPa]	Error f_R.2	f_R.3 [MPa]	Error f_R.3	f_R.4 [MPa]	Error f_R.4
M32	Exp.	2.38	42.66%	2.69	45.00%	2.76	44.92%	2.74	45.17%
M32	Predicted	4.15	42.66%	4.89	45.00%	5.01	44.92%	5.00	45.17%
M34	Exp.	5.29	0.68%	6.56	7.32%	7.00	16.18%	6.98	19.92%
M34	Predicted	5.33	0.68%	6.11	7.32%	6.03	16.18%	5.82	19.92%
M36	Exp.	7.29	12.17%	8.25	12.54%	8.04	14.27%	7.82	17.76%
M36	Predicted	6.50	12.17%	7.33	12.54%	7.04	14.27%	6.64	17.76%
M38	Exp.	6.82	18.99%	9.39	1.02%	9.51	6.28%	9.17	11.23%
M38	Predicted	8.42	18.99%	9.49	1.02%	8.95	6.28%	8.24	11.23%
M42	Exp.	3.26	22.11%	4.62	6.38%	4.26	15.70%	3.56	29.28%
M42	Predicted	4.19	22.11%	4.93	6.38%	5.05	15.70%	5.03	29.28%
M44	Exp.	4.89	12.75%	6.67	3.21%	6.47	1.70%	5.42	11.33%
M44	Predicted	5.60	12.75%	6.46	3.21%	6.36	1.70%	6.11	11.33%
M46	Exp.	6.16	8.71%	8.11	6.11%	7.21	1.72%	6.08	11.90%
M46	Predicted	6.75	8.71%	7.64	6.11%	7.34	1.72%	6.90	11.90%
M48	Exp.	9.08	9.93%	9.70	4.44%	8.94	2.09%	7.56	9.54%
M48	Predicted	8.26	9.93%	9.29	4.44%	8.76	2.09%	6.90	9.54%

Concrete Mixture	$f_{c}$ [MPa]	l [mm]	d [mm]	l/d	Fiber volume content (%)
10	45.60	35	0.55	63.64	0.75
11	56.39	35	0.55	63.64	0.75
12	61.23	35	0.55	63.64	0.75
13	61.94	35	0.55	63.64	0.75
16	60.66	35	0.55	63.64	0.75
17	63.46	35	0.55	63.64	0.75
18	54.81	35	0.55	63.64	0.75
19	64.83	35	0.55	63.64	0.75

Concrete Mix		Experimental data obtained by Lameiras et al. (2015) vs. Values predicted by the proposed equations
Concrete Mix		f_R.1 [MPa]	Error f_R.1	f_R.2 [MPa]	Error f_R.2	f_R.3 [MPa]	Error f_R.3	f_R.4 [MPa]	Error f_R.4
10	Exp.	9.21	24.95%	8.11	4.03%	6.82	15.84%	5.70	24.35%
10	Predicted	7.37	24.95%	8.45	4.03%	8.10	15.84%	7.54	24.35%
11	Exp.	8.22	2.84%	7.13	27.40%	5.42	42.46%	4.13	52.41%
11	Predicted	8.46	2.84%	9.82	27.40%	9.42	42.46%	8.68	52.41%
12	Exp.	7.44	16.55%	6.67	35.81%	5.52	44.63%	4.61	49.64%
12	Predicted	8.91	16.55%	10.39	35.81%	9.97	44.63%	9.15	49.64%
13	Exp.	6.82	24.05%	6.25	40.33%	5.38	46.45%	4.69	49.15%
13	Predicted	8.98	24.05%	10.47	40.33%	10.05	46.45%	9.22	49.15%
16	Exp.	6.67	24.74%	5.97	42.18%	5.26	46.90%	4.54	50.10%
16	Predicted	8.86	24.74%	10.33	42.18%	9.91	46.90%	9.10	50.10%
17	Exp.	8.39	7.99%	7.59	28.71%	6.52	36.17%	5.66	39.58%
17	Predicted	9.12	7.99%	10.65	28.71%	10.21	36.17%	9.37	39.58%
18	Exp.	8.36	0.63%	7.47	22.42%	6.40	30.70%	5.59	34.37%
18	Predicted	8.31	0.63%	9.63	22.42%	9.24	30.70%	8.52	34.37%
19	Exp.	6.62	28.37%	6.01	44.36%	5.16	50.21%	4.55	46.58%
19	Predicted	9.24	28.37%	10.80	44.36%	10.36	50.21%	8.52	46.58%

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[1] Corresponding author: Matheus Galvão Cardoso. E-mail: matheus-ssdo@hotmail.com