Influence of low content of steel fibre on concretes produced with recycled coarse aggregates with varying densities

Figueiredo, Antonio Domingues de; Pietra, Ivie; Bitencourt Júnior, Luís Antônio Guimarães

doi:10.1590/1517-7076-RMAT-2023-0109

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Articles • Matéria (Rio J.) 28 (2) • 2023 • https://doi.org/10.1590/1517-7076-RMAT-2023-0109 copy

Influence of low content of steel fibre on concretes produced with recycled coarse aggregates with varying densities

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The use of construction and demolition (C&D) waste as aggregate in concrete results in a reduction in strength due to its porosity. To compensate, mix designs often require higher cement contents, which increase the material’s environmental impact. This study presents an experimental and numerical analysis of the effect of steel fibres on the mechanical properties of the concrete produced with recycled C&D aggregates with varying densities. The variation in fibre content did not present any influence on the compressive strength of concrete, which is significantly affected by the lower density of the recycled C&D aggregate. The fibres collaborate to mitigate the loss of flexural strength of the steel fibre reinforcement in recycled coarse aggregate concrete (SFRRCAC) provoked by lower density of recycled aggregates when the water-to-cement ratio is lower. When the water-to-cement ratio is above 0.65, there is a great reduction of the matrix strengths due to the paste porosity and the influence of aggregate density and fibre content was insignificant.

KEYWORDS
concrete; recycled aggregates; steel fibres; experimental tests; numerical analyses

PHASE	1.9 < D < 2.2 (%)	2.2 < D < 2.5 (%)
Concrete and mortar	92.37	53.15
Red ceramic	2.43	0.18
White ceramic	2.81	0.17
Granite	0.48	44.91
Bitumen	1.73	1.59
Asbestos	0.18	0.00
Total	100.00	100.00

COARSE AGGREGATE	RECYCLED 1.9–2.2 g/cm³	RECYCLED 2.2–2.5 g/cm³	ORDINARY
Density (g/cm³)	2.07	2.50	2.63
Water absorption (%) in 24 hours	6.75	2.16	0.03
Maximum size (mm)	19	19	19

COARSE AGGREGATE	RECYCLED 2.07 g/cm³	RECYCLED 2.50 g/cm³	ORDINARY 2.63 g/cm³
α	54%	52%	48%

AGGREGATE ENVELOPE DENSITY	MIX PROPORTION NUMBER	CEMENT CONSUMPTION (kg/m³)	MATERIAL MASS PROPORTION TO CEMENT				FIBRE CONTENT (kg/m³–%)
			CEMENT	AGGREGATES		WATER
			CEMENT	FINE (A)	COARSE (B)
Recycled 2.07 g/cm³	1	474	1	1.16	1.84		0.41	0 – 0%
	2	346	1	1.97	2.53	0.57
	3	269	1	2.78	3.22	0.74
	4	474	1	1.16	1.84	0.43	10 – 0.13%
	5	346	1	1.97	2.53	0.57
	6	269	1	2.78	3.22	0.74
	7	474	1	1.16	1.84	0.47	20 – 0.25%
	8	346	1	1.97	2.53	0.57
	9	269	1	2.78	3.22	0.75
	10	474	1	1.16	1.84	0.47	40 – 0.51%
	11	346	1	1.97	2.53	0.60
	12	269	1	2.78	3.22	0.79
Recycled 2.50 g/cm³	13	533	1	1.08	1.92	0.36	0 – 0%
	14	391	1	1.86	2.64	0.45
	15	301	1	2.64	3.36	0.64
	16	533	1	1.08	1.92	0.36	10 – 0.13%
	17	391	1	1.86	2.64	0.46
	18	301	1	2.64	3.36	0.65
	19	533	1	1.08	1.92	0.37	20 – 0.25%
	20	391	1	1.86	2.64	0.48
	21	301	1	2.64	3.36	0.63
	22	533	1	1.08	1.92	0.37	40 – 0.51%
	23	391	1	1.86	2.64	0.48
	24	301	1	2.64	3.36	0.65
Ordinary 2.63 g/cm³	25	543	1	0.92	2.08	0.35	0 – 0%
	26	395	1	1.64	2.86	0.48
	27	310	1	2.36	3.64	0.61
	28	543	1	0.92	2.08	0.34	10 – 0.13%
	29	395	1	1.64	2.86	0.48
	30	310	1	2.36	3.64	0.61
	31	543	1	0.92	2.08	0.36	20 – 0.25%
	32	395	1	1.64	2.86	0.48
	33	310	1	2.36	3.64	0.60
	34	543	1	0.92	2.08	0.39	40 – 0.51%
	35	395	1	1.64	2.86	0.48
	36	310	1	2.36	3.64	0.61

CONCRETE PARAMETERS	RECYCLED 2.07 g/cm³	ORDINARY 2.63 g/cm³
Young’s modulus (MPa)	21000	35000
Poisson’s ratio	0.2	0.2
Fracture energy (N/mm)	0.15	0.15
Tensile strength (MPa)	2.10	2.88
Compression stress damage threshold (MPa)	21.0	28.8
Compressive parameter A-	0.89	0.89
Compressive parameter B-	1.16	1.16

AGGREGATE DENSITY (g/cm³)	CEMENT CONSUMPTION (kg/m³)	YOUNG’S MODULUS (GPa)
2.07	474	20.8
	346	19.4
	269	15.8
2.50	533	27.1
	391	26.4
	301	21.1
2.63	543	30.8
	395	27.6
	310	22.8

CONCRETE-FIBRE INTERACTION PARAMETERS	RECYCLED 2.07 g/cm³	ORDINARY 2.63 g/cm³
Maximum shear stress (MPa)	12.0	12.0
Residual shear stress (MPa)	4.5	4.5
α	0.4	0.4
Slip s₁ (mm)	0.01	0.01
Slip s₂ (mm)	6.5	6.5
coupling constant (normal) (MPa/mm)	10⁹	10⁹
coupling constant (tangential) (MPa/mm)	10³	10³

AGGREGATE ENVELOPE DENSITY	MIX PROPORTION NUMBER	SPECIFIC GRAVITY MASS OF CONCRETE (g/cm³)	WATER ABSORTION (%)	COMPRESSIVE STRENGTH (MPa)	FLEXURAL STRENGTH (MPa)
Recycled 2.07 g/cm³	1	2.08	8.90 ± 0.25	38.47 ± 0.06	4.27 ± 0.11
	2	2.03	9.46 ± 0.11	29.20 ± 1.04	3.75 ± 0.25
	3	2.05	9.78 ± 0.17	20.38 ± 0.03	3.01 ± 0.17
	4	2.17	9.34 ± 0.01	38.83 ± 0.88	4.50 ± 0.46
	5	2.11	9.80 ± 0.04	28.46 ± 0.17	3.99 ± 0.32
	6	2.07	10.10 ± 0.16	21.16 ± 0.68	3.05 ± 0.34
	7	2.17	9.41 ± 0.22	35.51 ± 3.60	4.58 ± 0.41
	8	2.13	9.54 ± 0.15	29.15 ± 0.20	3.96 ± 0.14
	9	2.09	9.96 ± 0.11	21.48 ± 1.26	3.19 ± 0.08
	10	2.19	9.22 ± 0.25	35.80 ± 0.66	4.90 ± 0.45
	11	2.16	9.62 ± 0.29	29.14 ± 2.48	3.98 ± 0.10
	12	2.14	10.47 ± 0.01	19.55 ± 1.48	3.17 ± 0.20
Recycled 2.50 g/cm³	13	2.33	6.49 ± 0.17	52.70 ± 2.53	5.70 ± 0.14
	14	2.29	6.72 ± 0.02	44.16 ± 4.49	4.60 ± 0.15
	15	2.24	7.04 ± 0.01	25.77 ± 0.16	3.52 ± 0.34
	16	2.35	6.75 ± 0.12	53.56 ± 3.57	6.11 ± 0.31
	17	2.27	7.21 ± 0.09	43.32 ± 1.27	4.63 ± 0.12
	18	2.20	7.39 ± 0.12	25.31 ± 0.02	3.52 ± 0.32
	19	2.34	6.77 ± 0.21	53.29 ± 4.19	5.95 ± 0.53
	20	2.29	7.10 ± 0.25	39.74 ± 0.70	5.05 ± 0.11
	21	2.26	7.36 ± 0.26	29.22 ± 1.79	3.84 ± 0.31
	22	2.35	6.68 ± 0.27	50.71 ± 1.15	6.12 ± 0.16
	23	2.33	6.81 ± 0.02	41.45 ± 1.43	5.28 ± 0.42
	24	2.27	7.23 ± 0.05	26.36 ± 2.91	3.70 ± 0.09
Ordinary 2.63 g/cm³	25	2.40	5.55 ± 0.05	54.79 ± 1.30	6.51 ± 0.65
	26	2.30	5.88 ± 0.16	40.24 ± 1.87	4.67 ± 0.21
	27	2.33	5.92 ± 0.06	31.09 ± 1.24	4.12 ± 0.42
	28	2.42	5.53 ± 0.15	55.44 ± 0.95	6.52 ± 0.45
	29	2.35	5.87 ± 0.14	43.72 ± 1.01	5.25 ± 0.05
	30	2.33	5.98 ± 0.01	30.67 ± 1.59	4.11 ± 0.21
	31	2.43	5.59 ± 0.23	54.10 ± 1.87	6.44 ± 0.66
	32	2.37	5.64 ± 0.09	41.66 ± 1.53	5.34 ± 0.21
	33	2.33	5.73 ± 0.24	30.51 ± 1.79	4.21 ± 0.42
	34	2.43	5.55 ± 0.29	49.15 ± 1.87	6.42 ± 0.14
	35	2.39	5.64 ± 0.19	43.90 ± 0.37	4.77 ± 0.45
	36	2.37	5.84 ± 0.09	30.86 ± 0.44	4.29 ± 0.47

Laboratório de Hidrogênio, Coppe - Universidade Federal do Rio de Janeiro, em cooperação com a Associação Brasileira do Hidrogênio, ABH2 Av. Moniz Aragão, 207, 21941-594, Rio de Janeiro, RJ, Brasil, Tel: +55 (21) 3938-8791 - Rio de Janeiro - RJ - Brazil
E-mail: revmateria@gmail.com

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[1] e-mail: antonio.figueiredo@usp.br, ivie@joycongero.com.br, luis.bitencourt@usp.br