Engineering behavior of ambient-cured geopolymer concrete activated by an alternative silicate from rice husk ash

Figures & data

Figure 1. SEM micrographs for: (a) grinded fly ash, (b) grinded blast furnace slag, (c) grinded rice husk ash.

Figure 2. Particle size distribution for the fine and coarse aggregates.

Table 1. Physical properties of fine and coarse aggregates.

Property	Coarse aggregate	Fine aggregate
Saturated-surface-dry density (kg/m³)	2316	2410
Compacted unit weight (kg/m³)	1430.25	1641.78
Moisture content (%)	0.705	3.348
Water absorption (%)	4.18	5.35

Table 2. Chemical composition of raw materials.

Compound	Fly ash, %	Slag, %	Rice husk ash, %	GU Cement, %
SiO2	51.30	33.70	90.93	20.80
Al2O3	20.70	12.80	0.11	4.70
Fe2O3	7.27	0.90	1.63	3.45
CaO	1.27	45.40	0.36	65.30
MgO	2.15	1.43	1.21	1.55
Na2O	0.36	0.12	0.02	0.40
K2O	3.07	1.93	2.90	0.15
P2O5	2.13	–	1.26	–
TiO2	2.72	0.92	–	–
MnO	1.62	–	–	–
SO3	2.53	–	–	2.75
Loss on ignition	4.90	2.80	1.60	0.90

Figure 3. X-ray diffraction patterns for raw materials.

Table 3. Mineralogical composition for raw materials.

Composition	Fly ash, %	Slag, %	Rice husk ash, %	GU Cement, %
Quartz	22.7	–	–	5.2
Mullite	15.4	–	–	–
Gehlenite	–	34.4	–	–
Magnesium oxide	–	2.9	–	2.6
Cristobalite	–	–	55.3	–
Tricalcium silicate	–	–	–	63.6
Dicalcium silicate	–	–	–	11.6
Tricalcium aluminate	–	–	–	6.7
Tetracalcium aluminoferrite	–	–	–	10.3
Amorphous content	61.9	62.7	44.7	–

Table 4. Proportions of concrete mixtures.

ID.	Cement (kg/m^3)	Fly ash (kg/m^3)	Slag (kg/m^3)	Coarse aggregate (kg/m^3)	Fine aggregate (kg/m^3)	Water (kg/m^3)	Sodium silicate (kg/m^3)	Sodium hydroxide (kg/m^3)	Rice husk ash (kg/m^3)
TC	459.0	–	–	971.6	608.2	206.0	–	–	–
GC	–	323.2	80.8	1010.0	606.0	–	207.98	82.90	–
GA	–	323.2	80.8	1010.0	606.0	–	–	325.83	58.17

Figure 4. (a) Appearance of cast concrete specimens, (b) typical failure after the compressive test. From left to right: TC, GA and GC concretes.

Figure 5. Calorimetric responses for pastes of concrete mixtures: (a) temperature increase vs. time, (b) cumulative heat vs. time, (c) heat flow vs. time (12 h), (d) heat flow vs. time (50 h).

Figure 6. X-ray diffraction patterns for geopolymer pastes from GC and GA concretes.

Table 5. Mineralogical composition for pastes from GC and GA concretes.

Composition	GC paste, %	GA paste, %
Quartz	7.06	15.26
Mullite	8.05	10.5
Gehlenite	1.69	–
Magnesium oxide	–	–
Cristobalite	–	5.18
Calcite	0.2	–
Natron*	–	44.37
Sodium carbonate beta*	–	0.22
Amorphous content	83	69.06

* Not considered in calculation of amorphous content.

Figure 7. Results of the concrete mixtures in the fresh state: (a) slump, (b) unit weight, (c) air content.

Figure 8. Flow curves for pastes from concrete mixtures.

Figure 9. Compressive strength evolution of TC, GC and GA concretes.

Table 6. Compressive strength of concretes at 28-day age, MPa.

ID	TC	GC	GA
Specimen 1	24.18	23.40	21.29
Specimen 2	24.49	22.56	20.88
Specimen 3	24.10	23.64	20.83
X, MPa	24.26	23.20	21.00
CV, %	0.7	0.5	1.0

Table 7. Input oxide molar ratios (input atomic ratios) of the GC and GA geopolymer concretes.

Molar ratio	GC	GA	Suggested values in the literature
			Kovalchuk et al. (2007)	Davidovits and J (2015)	Talling and Brandstetr (1989)
Na2O/Al2O3 (Na/Al)*	1.21	3.09	1.0	–	–
Na2O/ SiO2 (Na/Si)	0.22 (0.44)	0.57 (1.14)	–	0.20–0.28	–
SiO2/Al2O3 (Si/Al)	5.51 (2.75)	5.49 (2.74)	3.50–4.00	3.50–4.50	1.66–10.0
CaO/SiO2 (Ca/Si)*	0.17	0.18	–	–	0.50–2.0

* Input oxide molar ratio equal to input atomic ratio.

Figure 10. Comparison between experimental evolution of compressive strength and theoretical models for: (a) GC concrete, (b) GA concrete.

Table 8. Constants used in predicting the compressive strength evolution of geopolymer concretes.

Type of concrete	Constant			$r$
	$a$	$b$	$c$
GC	1.2319	0.1024	−0.1069	0.98
GA	1.3582	0.0064	−0.8207	0.97

Table 9. Modulus of elasticity of concretes at 28-day age, MPa.

ID	TC	GC	GA
Specimen 1	23148	9426	17933
Specimen 2	22780	10690	18512
Specimen 3	22994	10206	17431
$X,\mathrm{ }\mathrm{MPa}$	22974	10107	17959
$X/\sqrt{f_c^{\prime }}$	4664	2098	3918
CV, %	0.7	5.1	2.5

Figure 11. Comparison between experimental and theoretical values of the modulus of elasticity for: (a) Portland cement concrete, (b) fly ash geopolymer concrete, (c) fly ash slag geopolymer concrete, (d) alkali-activated slag concrete.

Table 10. Poisson’s ratios of concretes at 28-day age.

ID	TC	GC	GA
Specimen 1	0.167	0.175	0.176
Specimen 2	0.156	0.183	0.190
Specimen 3	0.164	0.185	0.182
$X,\mathrm{ }\mathrm{MPa}$	0.162	0.181	0.183
CV, %	2.9	2.4	3.1

Figure 12. Comparison between experimental and theoretical values of splitting tensile capacity for: (a) Portland cement concrete, (b) fly ash geopolymer concrete, (c) fly ash slag geopolymer concrete, (d) alkali-activated slag concrete.

Table 11. Splitting tensile strength of concretes at 28-day age, MPa.

ID	TC	GC	GA
Specimen 1	1.464	2.052	2.125
Specimen 2	1.675	2.047	2.062
Specimen 3	1.589	2.057	2.213
$X,\mathrm{ }\mathrm{MPa}$	1.576	2.052	2.133
$X/\sqrt{f_c^{\prime }}$	0.320	0.426	0.465
CV, %	5.5	0.2	2.9

Figure 13. SEM micrographs of pastes from manufactured concretes: (a) TC (50 μm), (b) GC (50 μm), (c) GA (50 μm), (d) TC (10 μm), (e) GC (5 μm), (f) GA (2 μm).

Figure 14. EDS analysis of pastes from manufactured concretes: (a) TC (spot a in Figure 13a) (b) GC (spot b in Figure 13b) (c) GA (spot c in Figure 13c).

Table A1. Existing models in the literature of modulus of elasticity for different types of concrete.

Type of concrete	Author	Equation [MPa]	Comments
Portland cement	ACI 318-19 (ACI 318–19, 2019)	$E=0.043{\rho }^{1.5}\sqrt{f_c^{\prime }}$	Concrete of unit weight between 1440 to 2560 kg/m^3
	CEB-FIP model code (1990)	$E=0.85\times 2.15\times {10}^4{\left(f_c^{\prime }/10\right)}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.}$	Concrete of normal weight
	EN-1992.1.1, (2004)	$E=22000{\left(f_c^{\prime }/10 \right)}^{0.3}$	Concrete of normal weight
Fly ash geopolymer	Prachasaree et al. (2014)	$E=840-886\sqrt{f_c^{\prime }}+647f_c^{\prime }$	- Class F fly ash - Curing of 60 °C/24 h
	Hardjito and Rangan (2005)	$E=2707\sqrt{f_c^{\prime }}+5300$	- Class F fly ash - Heat - steam curing up to 90 °C/24 h and ambient curing
	Diaz-Loya et al. (2011)	$E=580\sqrt{f_c^{\prime }}$	- Class C and F fly ash - Curing of 60 °C/72 h
		$E=0.037{\rho }^{1.5}\sqrt{f_c^{\prime }}$
	Tempest (2010)	$E=3421\sqrt{f_c^{\prime }}$	- Class F fly ash - Curing of 60 °C/24 h
	Islam et al. (2014)	$E=771.4f_c^{\prime 0.929}$	- Class C and F fly ash - Curing of 60 °C/24 h
Fly ash slag geopolymer	Nath and Sarker (2017)	$E=3510\sqrt{f_c^{\prime }}$	- Replacement of slag up to 15% wt. - Curing at room temperature
	Lee and Lee (2013)	$E=5300\sqrt[3]{f_c^{\prime }}$	- Class F fly ash - Replacement of slag up to 30% wt. - Curing at room temperature
	Singh et al. (2016)	$E=1228f_c^{\prime 0.891}$	- Class F fly ash - Replacement of slag up to 33% wt. - Curing at room temperature
Alkali-activated slag	Thomas and Peethamparan (2015)	$E=2900f_c^{\prime \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$5$}\right.}$	- Slag and Class C fly ash - Curing at room temperature and 50 °C
		$E=4400\sqrt{f_c^{\prime }}$
	Yang et al. (2012)	$E=4600{\left(\rho /2200\right)}^{1.5}\sqrt{f_c^{\prime }}$	- Curing at room temperature

Table B1. Existing models in the literature of splitting tensile strength for different types of concrete.

Type of concrete	Author	Equation [MPa]	Comments
Portland cement	ACI 318–19, (2019)	$f_t=$0.56$\sqrt{f_c^{\prime }}$	For f’c > 21 MPa
	CEB-FIP model code (1990)	$f_t=0.301f_c^{\prime 0.67}$	For f’c > 21 MPa
	EN-1992.1.1, (2004)	$f_t=0.3f_c^{\prime ⅔}$	For f’c < 50 MPa
Fly ash geopolymer	Albitar et al. (2015)	$f_t=0.60\sqrt{f_c^{\prime }}$	- Class F fly ash - Curing of 70 °C/24 h
	Hardjito and Rangan (2005)	$f_t=0.70\sqrt{f_c^{\prime }}$	- Class F fly ash - Heat and steam curing up to 90 °C/24h
	Nguyen et al. (2016)	$f_t=0.858f_c^{\prime 0.410}$	- Class F fly ash - Curing up to 120 °C/10 h
	Tempest (2010)	$f_t=0.616\sqrt{f_c^{\prime }}$	- Class F fly ash - Curing of 60 °C/24 h
	Ryu et al. (2013)	$f_t=0.17f_c^{\prime ¾}$	- Class F fly ash - Curing of 60 °C/24 h
Fly ash slag geopolymer	Neupane (2016)	$f_t=0.67\sqrt{f_c^{\prime }}$	- Class F fly ash - Replacement of slag up to 40% wt. - Curing at room temperature
	Lee and Lee (2013)	$f_t=0.45\sqrt{f_c^{\prime }}$	- Class F fly ash - Replacement of slag up to 30% wt. - Curing at room temperature
	Sofi et al. (2007)	$f_t=0.48\sqrt{f_c^{\prime }}$	- Class F fly ash - Replacement of slag up to 70% wt. - Curing at room temperature
	Ding et al. (2016)	$f_t=0.527\sqrt{f_c^{\prime }}$	- Class F fly ash - Curing at room temperature
		$f_t=0.163f_c^{\prime 0.818}$
Alkali-activated slag	Thomas and Peethamparan (2015)	$f_t=\raisebox{1ex}{$2$}\!\left/ \!\raisebox{-1ex}{$5$}\right.f_c^{\prime \raisebox{1ex}{$7$}\!\left/ \!\raisebox{-1ex}{$9$}\right.}$	- Slag and Class C fly ash - Curing at room temperature and 50 °C
		$f_t=1.08\sqrt{f_c^{\prime }}$
	Yang et al. (2012)	$f_t=0.30f_c^{\prime 0.65}$	- Curing at room temperature

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Data availability statement

Data available within the article or its supplementary materials.