Effect of sea sand and recycled aggregate replacement on fly ash/slag-based geopolymer concrete

Weiwen Li; Xinlin Huang; Jiali Zhao; Yujie Huang; Eskinder Desta Shumuye; Xu Yang

doi:10.2478/msp-2021-0049

Figures & Tables

Aggregate used in this research. (A) Coarse aggregate. (B) Fine aggregate

Factors affecting splitting tensile strength

Compressive strength of paste and mortar

Failure mode of the SS group. (A) SG-0, (B) SG-25, (C) SG-50, (D) SG-75, (E) SG-100, (F) SPC-100. SS, sea sand

Fracture surface of specimens. (A) Fracture surface of NA, (B) Fracture surface of RA. NA, natural aggregate; RA, recycled aggregate

Failure mode of RS group. (A) RG-0, (B) RG-50, (C) RG-100, (D) RPC-100. RS, river sand

Influence of RA replacement ratio and sand types on compressive strength. RA, recycled aggregate

SEM photos of SS group at 7 days. (A) SG-0, (B) SG-50, (C) SG-100. SEM, scanning electron microscopy. SS, sea sand

SEM photos of SS group at 28 days. (A) SG-0, (B) SG-25, (C) SG-50, (D) SG-75, (E) SG-100. FA, fly ash; ITZ, interface transportation zone; SEM, scanning electron microscopy; SS, sea sand

SEM photos of RS group at 7 days. (A) RG-0, (B) RG-50, (C) RG-100. RS, river sand. ITZ, interface transportation zone; SEM, scanning electron microscopy

Influence of RA replacement ratio and sand types on elastic modulus. RA, recycled aggregate

Stress–strain curves at 7 days. (A) SS–GPC, (B) RS–GPC. RS–GPC, river sand geopolymer concrete; SS–GPC, sea sand geopolymer concrete

Stress–strain curves at 28 days. (A) SS–GPC, (B) RS–GPC. RS, river sand geopolymer concrete; SS–GPC, sea sand geopolymer concrete

Comparison of GPC and ordinary silicate concrete. (A) 7 days, (B) 28 days. GPC, geopolymer concrete

Influence of RA replacement ratio and sand types on splitting tensile strength. RA, recycled aggregate

Influence of RA replacement ratio and sand types on flexural strength. RA, recycled aggregate

Mixture proportions of two-factor test (kg/m3)

NO.	FA	Slag	Sand	NA	RA	NaOH solution	Na₂SiO₃ solution	RA replacement rate	Type of sand	Combined components
SG-0	375.7	161.1	454.4	1,058.7	0	70	175	0	SS	Geopolymer
SG-25	375.7	161.1	454.4	794.1	264.7	70	175	25%	SS	Geopolymer
SG-50	375.7	161.1	454.4	529.4	529.4	70	175	50%	SS	Geopolymer
SG-75	375.7	161.1	454.4	264.7	794.1	70	175	75%	SS	Geopolymer
SG-100	375.7	161.1	454.4	0	1,058.7	70	175	100%	SS	Geopolymer
RG-0	375.7	161.1	454.4	1,058.8	0	70	175	0	RS	Geopolymer
RG-50	375.7	161.1	454.4	529.4	529.4	70	175	50%	RS	Geopolymer
RG-100	375.7	161.1	454.4	0	1,058.8	70	175	100%	RS	Geopolymer
	Portland Cement					Distilled water
SPC-100	536.8		454.4	0	1,058.8	161.1		100%	SS	Portland cement
RPC-100	536.8		454.4	0	1,058.8	161.1		100%	RS	Portland cement

Mixture proportion of orthogonal test (kg/m3)

Test number	FA	Slag	SS	NA	NaOH solution	Na₂SiO₃ solution	Slag content (%)	Water-binder ratio	NaOH solution concentration
1	499	55	449	1,047	70	175	10	0.3	8 mol/L
2	322	81	495	1,153	70	175	20	0.4	12 mol/L
3	219	94	522	1,215	70	175	30	0.5	16 mol/L
4	266	66	516	1,202	70	175	20	0.5	8 mol/L
5	376	161	454	1,058	70	175	30	0.3	12 mol/L
6	352	39	498	1,160	70	175	10	0.4	16 mol/L
7	291	125	491	1,144	70	175	30	0.4	8 mol/L
8	290	32	519	1,209	70	175	10	0.5	12 mol/L
9	417	104	459	1,070	70	175	20	0.3	16 mol/L

Basic performance index of aggregate

Aggregate type	Particle size (mm)	Apparent density (kg/m³)	Bulk density (kg/m³)	Water absorption (%)	Crushing index (%)
Natural coarse aggregate	5–20	2,780	1,420	0.15	9.22
Recycled coarse aggregate	5–20	2,250	1,380	6.07	15.97

Main chemical composition of FA and slag

Combined components	Loss on ignition (%)	CaO (%)	SiO₂ (%)	Al₂O₃ (%)	MgO (%)	Fe₂O₃ (%)	SO₃ (%)
FA	3.79	6.66	42.34	25.84	1.17	5.46	0.95
Slag	0.34	34.45	27.46	16.24	8.46	0.42	0.81

Mixture proportions of paste and mortar (kg/m3)

No.	FA	Slag	SS	RS	NaOH solution	Na₂SiO₃ solution
Seawater paste	840	360	0	0	156^*	391
DWP	840	360	0	0	156	391
SSM	840	360	600	0	156	391
RSM	840	360	0	600	156	391

Chemical properties of sodium silicate solution

Modulus	Baume degree (Be)	Na₂O (wt.%)	SiO₂ (wt.%)	H₂O (wt.%)
3.12	40	8.5	26.5	65

NaOH solution formulation

Molarity	Proportion of NaOH solids (wt.%)	Proportion of distilled water (wt.%)
8 mol/L	25.1	74.9
12 mol/L	32.43	67.57
16 mol/L	39.02	60.98

Average values of various factors in orthogonal test

Variables and grades	3 days compressive strength/MPa	28 days compressive strength/MPa	28 days splitting tensile strength/MPa	Cylinder compressive strength/MPa	Elastic modulus/GPa	Slump/mm	Poisson’s ratio
A1	10.28	21.05	1.21	17.55	9.20	235	0.21
A2	15.38	29.03	1.36	27.07	11.20	237	0.23
A3	15.41	29.89	1.53	22.53	9.50	230	0.18
B1	8.29	19.09	1.21	17.12	9.03	231	0.22
B2	14.25	27.75	1.39	21.65	10.30	236	0.18
B3	18.54	33.14	1.50	28.38	10.57	235	0.22
C1	19.32	35.92	1.67	29.34	13.57	208	0.15
C2	12.29	24.40	1.37	22.90	9.50	239	0.24
C3	9.47	19.65	1.06	14.91	6.83	256	0.24

Test results of two-factor test

NO.	Compressive strength/MPa		Flexural strength/MPa		Splitting tensile strength/MPa		Elastic modulus/GPa		Poisson’s ratio		Slump
NO.	7 days	28 days	7 days	28 days	7 days	28 days	7 days	28 days	7 days	28 days	Slump
SG-0	44.92	61.67	2.98	4.13	1.24	1.73	12.6	20.3	0.25	0.21	240
SG-25	43.24	60.10	3.07	3.92	1.26	1.65	12.8	20.5	0.19	0.23	250
SG-50	43.92	61.97	3.13	3.95	1.33	1.58	14.0	20.7	0.16	0.17	254
SG-75	42.67	60.43	3.11	3.81	1.30	1.52	12.5	18.8	0.19	0.21	255
SG-100	42.64	54.80	3.08	3.70	1.31	1.44	13.9	18.1	0.13	0.30	260
RG-0	55.79	66.60	3.60	4.47	1.63	1.73	15.6	23.8	0.19	0.30	235
RG-50	49.89	57.83	2.65	2.95	1.35	1.50	8.8	17.4	0.20	0.30	245
RG-100	44.94	49.50	2.34	2.53	1.10	1.18	6.6	11.1	0.25	0.22	250
SPC-100	38.88	44.23	3.87	4.24	1.33	1.50	24.1	25.9	0.24	0.13	115
RPC-100	30.74	35.93	3.02	3.53	1.33	1.28	23.9	25.1	0.09	0.19	110

Effect of sea sand and recycled aggregate replacement on fly ash/slag-based geopolymer concrete

Figures & Tables

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Mixture proportions of two-factor test (kg/m3)

Mixture proportion of orthogonal test (kg/m3)

Basic performance index of aggregate

Main chemical composition of FA and slag

Mixture proportions of paste and mortar (kg/m3)

Chemical properties of sodium silicate solution

NaOH solution formulation

Average values of various factors in orthogonal test

Test results of two-factor test

Paradigm

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