Study of the influence of the mortar fine recycled aggregate ratio and the mixing sequence on the behavior of new mortars

Silva Neto, Gilberto Alves da; Leite, Mônica Batista

doi:10.1590/s1678-86212018000200242

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Tecnologia das Argamassas • Ambient. constr. 18 (2) • Apr-Jun 2018 • https://doi.org/10.1590/s1678-86212018000200242 copy

Study of the influence of the mortar fine recycled aggregate ratio and the mixing sequence on the behavior of new mortars

Estudo da influência do teor de agregrado miúdo reciclado de argamassa e da sequência de mistura no comportamento de novas argamassas

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The objective of this study was to investigate the behavior of mortars by replacing a natural fine aggregate (NFA) with mortar fine recycled aggregate (MFRA), with dimensions of less than 2.4mm. In addition, the influence of the mixing sequence over the performance of these mortars was analyzed. For this purpose, the replacement contents, by weight, of 20% and 40%, and two mixing sequences were adopted: the sequence of the Brazilian Standard, NBR 7215 (ABNT, 1996ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 7215: cimento Portland: determinação da resistência à compressão. Rio de Janeiro, 1996.) and an adaptation for mortars (MDE, in Portuguese, Mistura em Duas Etapas) of the Two-Stage Mixing Approach (TSMA), proposed by Tam, Gao and Tam (2005)TAM, V. W. Y.; GAO, X. F.; TAM, C. M. Micro-Structural Analysis of Recycled Aggregate Concrete Produced From Two-Stage Mixing Approach. Cement Concrete Research, v. 35, p. 1195-1203, 2005. for recycled concrete. The mortars were produced with cement CPV-ARI, using a mixing proportion of 1.0:5.0 (cement:aggregate, by weight) and a constant water/cement rate of 0.88. To analyze the behavior of the recycled mortars, they were tested in the fresh state and in the hardened state. The study concluded that the partial replacement of the NFA with the MFRA improved some properties of the recycled mortars: the air entrained content and the water absorption rate by capillarity decreased, and the mechanical performance increased. Regarding the influence of the mixing sequence, the adoption of the MDE promoted a better behavior on the mortar properties evaluated.

Keywords:
Recycled mortar; Mixing sequence; Mortar fine recycled aggregate

Evaluated Properties - Methods	Natural NFA	Recycled MFRA
Maximum size aggregate (mm) - NBR NM 248(ABNT, 2003ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR NM 248: agregado: determinação da composição granulométrica. Rio de Janeiro, 2003.)	1.20	2.40
Fineness Modulus - NBR NM 248 (ABNT, 2003ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR NM 248: agregado: determinação da composição granulométrica. Rio de Janeiro, 2003.)	1.77	1.88
Specific Gravity (g/cm³) - NBR 52 (ABNT, 2009ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR NM 52: agregado miúdo: determinação da massa específica e massa específica aparente. Rio de Janeiro, 2009.)	2.62	2.48
Water Absorption (%) - NBR NM 30 (2003)ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR NM 30: agregado miúdo: determinação da absorção de água. Rio de Janeiro, 2001.	0.1	7.2
Fine content (%) - NBR NM 46 (ABNT, 2003ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR NM 46: agregados: determinação do material fino que passa através da peneira 75 µm, por lavagem. Rio de Janeiro, 2003.)	2.1	10.9

	REF		20% MFRA		40% MFRA
	NBR 7215	MDE	NBR 7215	MDE	NBR 7215	MDE
A10 At ± SD (CV) g/cm² ± g/cm² (%)	0.28±0.01 (3.7)	0.25±0.01 (2.7)	0.28±0.01 (3.5)	0.25±0.01 (5.4)	0.26±0.02 (6.2)	0.22±0.01 (4.3)
A90 At ± SD (CV) g/cm² ± g/cm² (%)	0.73±0.01 (1.2)	0.70±0.03 (4.2)	0.69±0.02 (2.6)	0.63±0.02 (3.4)	0.66±0.02 (3.2)	0.52±0.03 (5.1)
C C ± SD (CV) g/dm².min^1/2±g/dm².min^1/2(%)	7.3±0.09 (1.2)	7.2±0.38 (5.3)	6.6±0.14 (2.2)	6.2±0.07 (1.1)	6.6±0.09 (1.4)	5.1±0.27 (5.2)

	REF		20% MFRA		40% MFRA
	NBR 7215	MDE	NBR 7215	MDE	NBR 7215	MDE
Water absorption rate (%) A ± SD (CV) % ± % (%)	13.54±0.73 (5.4)	13.49±0.42 (3.1)	13.17±0.20 (1.5)	13.31±0.32 (2.4)	13.19±0.41 (3.1)	12.82±0.17 (1.4)
Void Index (%) I_V ± SD (CV) % ± % (%)	25.4±1.15 (4.5)	25.2±0.71 (2.8)	24.6±0.30 (1.2)	24.9±0.56 (2.3)	24.8±0.69 (2.8)	23.7±0.33 (1.4)
Specific gravity ρ ± SD (CV) g/cm³ ± g/cm³ (%)	2.52±0.02 (0.8)	2.50±0.02 (0.8)	2.48±0.00 (0.2)	2.49±0.02 (0.8)	2.50±0.02 (0.8)	2.43±0.02 (0.8)

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[1] Gilberto Alves da Silva Neto

Departamento de Tecnologia, Laboratórios de Tecnologia | Universidade Estadual de Feira de Santana | Av. Transnordestina, s/n, Campus Universitário, Novo Horizonte | Feira de Santana - BA - Brasil | CEP 44036-900 | Tel.: (75) 3625-8549 | E-mail: gilbertoalves.eng@gmail.com

Consistence Index
Mixing Sequence	REF C ± SD (CV)vmm ± mm (%)	20%MFRA C ± SD (CV)vmm ± mm (%)	40%MFRA C ± SD (CV)vmm ± mm (%)
NBR 7215	270 ± 1.1 (0.4)	265 ± 0.2 (0.1)	243 ± 0.5 (0.2)
MDE	276 ± 0.2 (0.1)	248 ± 1.4 (0.6)	230 ± 5.7 (2.5)
Water Retentivity
Mixing Sequence	REF Ra ± SD (CV) % ± % (%)	20%MFRA Ra ± SD (CV) % ± % (%)	40%MFRA Ra ± SD (CV) % ± % (%)
NBR 7215	64±0.0 (0.1)	68±0.8 (1.1)	74±2.2 (2.9)
MDE	64±0.9 (1.4)	69±0.9 (1.3)	74±0.6 (0.9)
Air Entrained Content
Mixing Sequence	REF A ± SD (CV) % ± % (%)	20%MFRA A ± SD (CV) % ± % (%)	40%MFRA A ± SD (CV) % ± % (%)
NBR 7215	8.2±0.32(3.9)	7.0±0.27(3.9)	5.5±0.64(11.6)
MDE	8.7±0.05(0.5)	7.0±0.06(0.8)	5.7±0.34(6.0)
Bulk Density
Mixing Sequence	REF d ± SD (CV) kg/m³ ± kg/m³ (%)	20%MFRA d ± SD (CV) kg/m³ ± kg/m³ (%)	40%MFRA d ± SD (CV) kg/m³ ± kg/m³ (%)
NBR 7215	2029±7.0(0.3)	2037±6.0(0.3)	2049±13.9(0.7)
MDE	2018±1.0(0.1)	2037±1.3(0.1)	2045±7.4(0.4)

Flexion
Mixing Sequence	REF f_t ± SD(CV) MPa ± MPa(%)		20%MFRA f_t ± SD(CV) MPa ± MPa(%)		40%MFRA f_t ± SD (CV) MPa ± MPa (%)
Mixing Sequence	7 days	28 days	7 days	28 days	7 days	28 days
NBR 7215	3.7±0.2(5.4)	4.2±0.4(8.3)	4.0±0.4(8.9)	6.0±0.3(4.2)	5.4±0.3(4.6)	5.8±0.3(4.5)
MDE	4.3±0.2(5.1)	6.1±0.1(1.2)	4.5±0.2(4.7)	6.3±0.2(2.7)	5.4±0.1(2.2)	6.9±0.5(7.2)
Compression
Mixing Sequence	REF f_c ± SD (CV) MPa ± MPa (%)		20%MFRA f_c ± SD (CV) MPa ± MPa (%)		40%MFRA f_c ± SD (CV) MPa ± MPa (%)
Mixing Sequence	7 days	28 days	7 days	28 days	7 days	28 days
NBR 7215	9.7±0.3(3.3)	13.5±0.4(2.8)	11.3±0.2(1.5)	14.9±0.3(2.1)	12.5±0.3(2.2)	17.5±0.3(2.0)
MDE	11.0±0.3(3.0)	14.3±0.2(1.6)	12.2±0.4(3.1)	16.2±0.3(1.8)	13.0±0.4(2.9)	16.7±0.4(2.3)

	Absorption rate - NBR 7215					Void Index - NBR 7215
Effects	DF	MS	F_c	F_0.05	Sg	DF	MS	F_c	F_0.05	Sg
% MFRA	2	0.133	0.546	5.14	NS	2	0.563	0.886	5.14	NS
ERROR	6	0.243				6	0.636
	Absorption rate - MDE					Void Index - MDE
Effects	DF	MS	F_c	F_0.05	Sg	DF	MS	F_c	F_0.05	Sg
% MFRA	2	0.362	3.51	5.14	NS	2	1.808	5.84	5.14	S
ERROR	6	0.103				6	0.31