Shrinkage and porosity in concretes produced with recycled concrete aggregate and rice husk ash

The admixture of recycled concrete aggregates (RCA) in new concretes is an interesting alternative in the efforts to mitigate environmental impacts. RCA may increase porosity and change properties of concretes. Rice husk ash (RHA) is employed as supplementary cementitious material may improve concrete properties. The present study investigated the shrinkage of concrete prepared with RCA and RHA, proposing a mathematical model to explain the phenomenon. Concretes were produced with 25% and 50% of coarse recycled aggregate as replacement of natural aggregate, 0%, 10%, and 20% of RHA as replacement of cement, and a water-to-binder ratio of 0.64. Water absorption and capillary and total porosities were analyzed on day 28. Shrinkage tests were conducted on days 1, 4, 7, 14, 28, 63, 91, and 112. The results point to a significant interaction between RHA and RCA.

Keywords:
recycled concrete aggregate; rice husk ash; shrinkage; porosity

Authorship

V. CECCONELLO

Unisinos, PPG em Engenharia Civil, São Leopoldo, RS, Brasil. vcecconello@gmail.com engenheirosartori@gmail.com marlovak@unisinos.br claudiok@unisinos.br mancio@unisinos.brUnisinosBrasilSão Leopoldo, RS, BrasilUnisinos, PPG em Engenharia Civil, São Leopoldo, RS, Brasil. vcecconello@gmail.com engenheirosartori@gmail.com marlovak@unisinos.br claudiok@unisinos.br mancio@unisinos.br

http://orcid.org/0000-0002-9323-795X

B. R. C.SARTORI

http://orcid.org/0000-0002-3517-1198

M. P .KULAKOWSKI

http://orcid.org/0000-0002-7661-3909

C. S. KAZMIERCZAK

http://orcid.org/0000-0001-7552-3867

M. MANCIO

http://orcid.org/0000-0002-0736-7249

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (9)
Tables (17)

Control factors	Study levels
RHA content (%)	0	10	20
RCA content (%)	0	25	50

Parameter	April 2012 batch	May 2012 batch
Al₂O₃ (%)	4.12	4.12
SiO₂ (%)	19.42	19.39
Fe₂O₃ (%)	2.60	2.59
CaO (%)	60.76	60.78
MgO (%)	4.85	4.93
SO₃ (%)	3.03	3.08
Loss on ignition (%)	6.04	6.08
Free CaO (%)	2.89	2.24
Insoluble fraction (%)	2	2
Alkaline equivalent (%)	0.63	0.62
Hot expansion (mm)	0.50	1.00
Initial setting time (h:min)	03:20	3:30
Final setting time (h:min)	04:30	4:30
Normal amount of water (%)	26.20	26.30
Blaine (cm²/g)	3.850	3.720
#200 (%)	3.4	4.2
#325 (%)	16.3	15.5
Comp. strength day 1 (MPa)	16.3	16.9
Comp. strength day 3 (MPa)	29.0	29.3
Comp. strength day 7 (MPa)	36.9	36.6
Comp. strength day 28 (MPa)	41.9	41.9
Specific weight (g/cm³)	3.11	3.11

Parameter	Content (%)
SiO₂	94.99
K₂O	1.01
SO₃	0.57
Cl	0.43
CaO	0.33
MnO	0.20
Al₂O₃	0.18
P₂O₅	0.10
Fe₂O₃	0.06
TiO₂	0.01
MgO	0.01
ZnO	0.00
P.F.	2.12

Test/standard	Value (g/cm³)
Unit weight/ NBR NM 45 - 2006	1.52
Specific weight/ NBR NM 52 - 2009	2.55

Mesh	Retained fraction (%)	Accumulated retained fraction (%)
6.3mm	1	1
4.8mm	2	3
2.4mm	5	8
1.2mm	6	14
0.6mm	11	25
0.3mm	38	63
0.15mm	35	98
<0.15mm	2	100
Maximum characteristic size (mm)	4.8 mm
Fineness modulus	2.12

Test/standard	Value (g/cm³)
Unit weight/ NM 45 - 2006	1.40
Specific weight/ NM 53 - 2009	2.67

Mesh	% retained fraction	% retained fraction (accumulated)
25 mm	0	0
19 mm	0	0
12.5 mm	39	39
9.5 mm	39	78
6.3 mm	22	100
<6.3 mm	0	100
Maximum diameter (mm)	19
Fineness modulus	6.78

Characteristic	Value
Density	1.07(g/cm³)
Percent amount used (considering cement amount)	0.2 to 5.0 (%)
Chlorides	< 0.1 (%)
Alkalis	< 1.0 (%)

RCA (%)	Absorption rate (mm/h^1/2)
	RHA (%)
	0	10	20
0	1.32	0.86	0.61
	1.26	0.87	0.66
	1.13	0.76	0.61
25	1.10	0.49	0.65
	1.18	1.00	0.53
	1.31	0.88	0.51
50	1.28	0.87	0.53
	1.03	0.80	0.53
	0.95	0.82	0.57

RCA (%)	Capillary porosity (%)
	RHA (%)
	0	10	20
0	13.1	0.86	0.61
0	12.8	11.8	0.66
25	12.8	5.7	0.61
25	12.9	10.9	0.66
50	12.4	6.8	4.5
50	11.4	6.9	4.5

RCA (%)	Total porosity (%)
	RHA (%)
	0	10	20
0	13.6	12.2	7.8
0	13.1	11.4	7.4
25	13.5	13.1	6.3
25	13.6	11.3	6.2
50	13.2	10.3	6.4
50	12.5	10.1	6.3

Source	df	SS	SM	F test	Significance - p
RHA	2	135.11096	67.555479	253.32696	0.000000
RCA	2	3.8944163	1.9472082	7.301855	0.013052
RHA*RCA	4	2.9600472	0.7400118	2.7749775	0.093741
Error	9	2.4000577	0.2666731	-	-

Mixtures		w:b ratio	Mean
Mixtures			Day 4	Day 7	Day 14	Day 28	Day 63	Day 91	Day 112
RHA (%)	RCA (%)		(µm)	(µm)	(µm)	(µm)	(µm)	(µm)	(µm)
0	0	-	-35.33	-51.67	-25.00	-16.00	14.00	31.00	21.33
		0.64	-23.33	-60.33	-23.67	-12.67	20.33	24.33	38.33
		-	-68.00	-25.00	-12.33	20.67	50.00	56.33	80.67
10	0	-	-12.00	-51.67	-10.67	31.00	58.67	66.67	81.67
		0.64	-31.00	-53.33	-14.00	20.00	50.33	63.33	51.00
		-	-10.00	-45.00	44.00	42.67	74.33	93.67	86.00
20	0	-	-10.00	-21.00	21.00	63.67	74.00	89.67	122.33
		0.64	-5.67	-11.67	26.33	63.00	108.67	101.33	122.33
		-	45.00	38.33	23.67	98.00	113.00	124.33	136.33
0	25	-	-54.00	47.33	-65.67	-32.67	-13.67	14.00	28.33
		0.64	-69.33	-64.33	-24.00	-3.00	23.00	33.00	42.00
		-	-61.67	-48.67	5.33	15.67	37.33	56.00	67.67
0	25	-	-54.00	47.33	-65.67	-32.67	-13.67	14.00	28.33
		0.64	-69.33	-64.33	-24.00	-3.00	23.00	33.00	42.00
		-	-61.67	-48.67	5.33	15.67	37.33	56.00	67.67
0	50	-	-25.33	-16.67	-1.67	13.33	30.17	59.33	47.67
		0.64	-18.67	-12.33	-13.33	1.00	28.67	57.33	61.33
		-	-8.67	-12.00	-8.00	31.00	57.33	61.67	93.00
10	25	-	48.67	-2.67	47.00	79.67	104.67	117.00	119.67
		0.64	-0.67	-3.00	22.67	34.67	95.00	73.67	83.33
		-	-15.00	-38.67	-22.33	33.33	88.00	74.33	64.33
10	50	-	31.33	-50.00	38.00	65.33	105.00	114.67	120.00
		0.64	40.00	2.33	39.33	74.00	113.67	125.00	131.00
		-	-33.67	-79.00	-32.00	69.67	109.33	119.83	125.50
20	25	-	-15.33	-22.67	25.67	27.33	68.67	105.33	78.67
		0.64	-6.33	-13.67	23.00	45.00	73.33	85.67	76.67
		-	-12.67	-28.00	0.67	15.67	74.67	80.67	59.33
20	50	-	-47.67	-19.00	3.00	11.67	47.33	73.33	44.00
		0.64	-32.67	-57.33	-15.33	4.00	54.33	63.00	63.00
		-	-2.00	-26.33	48.00	44.33	67.00	101.00	112.33

Source	Df	SS	SM	F test	Significance - p
Model	7	5.50E-01	7.86E-02	1.15E+02	0
Residual	182	1.24E-01	0.0006824	-	-
Total	189	6.74E-01	-	-	-
Adjusted total	188	5.01E-01	-	-	-

Factor	Parameter	Estimate	Standard error	T Test	p
Constant	bo	7.1793	1.36472	5.2606469	0.000000
RHA	b1	-0.0043	0.00132094	3.2596711	0.000000
RCA	b2	7.2241	1.36559	5.2900871	0.000000
AGE	b3	0.00103	5.72213E-05	18.038388	0.000000
RHA*RCA	b12	-7223.6	1365.63	5.2896026	0.000000
CCA*AGE	b13	-0.00002	9.52372E-06	1.9893382	0.023572
RCA*AGE	b23	-0.0071	0.0013389	5.3323923	0.000000

Mixtures		Day 28 (MPa)	Day 63 (MPa)	Day 112 (MPa)
RCA (%)	RHA (%)	Day 28 (MPa)	Day 63 (MPa)	Day 112 (MPa)
0	0	24.4	26.3	27.0
0	10	26.6	31.4	31.4
0	20	29.1	29.3	31.5
25	0	20.4	19.4	22.6
25	10	22.9	28.8	34.3
25	20	23.3	32.7	36.9
50	0	25.0	30.6	30.2
50	10	27.1	31.4	30.1
50	20	30.5	32.4	35.5