Geopolymer-stabilized soils: influencing factors, strength development mechanism and sustainability

Figures & data

Figure 1. Geopolymerization (a) process and (b) sequence

Table 1. Soil properties.

LL (%)	PL (%)	PI (%)	MDD (g/cc)	OMC (%)	USCS classification	Reference
52	22	30	1.67	18.6	CH	Current study
116	27	89	1.41	23.8	CH	[45]
82	25	57	1.52	19.2	CH	[45]
37	23	14	1.65	19	CL	[45]

Figure 2. SEM images (a) FA and (b) S.

Figure 3. Sample preparation and testing.

Figure 4. Heat map.

Figure 5. Structure of the RF model.

Figure 6. Hyperparameters tunning.

Table 2. Compaction results of the stabilized expansive clays.

Cement-treated clays
OPC content (%)	4	8	12	16	20
OMC (%)	18.4	17.6	16.3	15.9	15.4
MDD (g/cc)	1.72	1.79	1.82	1.85	1.89
Geopolymer soil with varying FA content (%)
Fly ash (%)	4	8	12	16	20
OAC (%)	18.3	17.9	17.4	16.9	16.6
MDD (g/cc)	1.65	1.62	1.59	1.57	1.53
Geopolymer soil with varying slag content (%)
Slag (%)	4	8	12	16	20
OAC (%)	18.6	18.1	17.7	17.2	16.8
MDD (g/cc)	1.71	1.77	1.84	1.87	1.91

Figure 7. Cement-treated clays stress–strain curves.

Table 3. UCS results of the stabilized expansive clays.

Cement-treated clays
OPC content (%)		4	8	12	16	20
Unconfined compressive strength (MPa) for curing periods of	7 days	0.21	0.34	0.57	1.09	1.74
	28 days	0.32	0.48	0.88	1.60	2.25
Geopolymer soil with varying FA content (%)
Fly ash (%)		4	8	12	16	20
Unconfined compressive strength (MPa) for curing periods of	7 days	0.19	0.84	1.14	1.56	1.85
	28 days	0.33	1.69	2.38	2.91	3.19
Geopolymer soil with varying slag content (%)
Slag (%)		4	8	12	16	20
Unconfined compressive strength (MPa) for curing periods of	7 days	0.24	1.25	1.85	2.11	2.45
	28 days	0.38	1.98	2.63	3.18	3.57

Figure 8. Fly ash-based geopolymer blended clays stress–strain curves.

Figure 9. Slag-based geopolymer blended clays stress–strain curves.

Figure 10. The effect of precursor content on UCS 28 days curing.

Figure 11. SEM images of the geopolymer soils blended with FA and S: (a) 8% FA, (b) 8% S, (c) 16% FA, (d) 16% S and (e) 20% S.

Table 4. Sustainability indices comparison of stabilized clays with OPC, fly ash-based geopolymers and slag-based geopolymers.

Additive content	OPC-treated soils	Fly ash-based geopolymer soils	Slag-based geopolymer soils
Cost-efficiency
4	0.0006	0.0003	0.0004
8	0.0004	0.0009	0.0015
12	0.0005	0.0008	0.0013
16	0.0007	0.0007	0.0012
20	0.0008	0.0006	0.001
Energy-efficiency
4	0.311	0.108	0.165
8	0.648	0.223	0.341
12	0.989	0.341	0.521
16	1.34	0.462	0.706
20	1.712	0.59	0.901
Eco-efficiency
4	0.057	0.021	0.024
8	0.12	0.044	0.051
12	0.183	0.067	0.077
16	0.248	0.091	0.105
20	0.317	0.116	0.134

Figure 12. CO₂ emissions of stabilized clays with (a) OPC, (b) fly ash-based geopolymers and (c) slag-based geopolymers.

Figure 13. UCS prediction with LR (a) training and (b) testing.

Table 5. Performance metrics comparison of various models.

	Training data				Test data
Regression technique	MAE	MSE	RMSE	R^2	MAE	MSE	RMSE	R^2
Linear Regression	2.18	6.90	2.63	0.83	2.21	7.36	2.71	0.83
KNN	0.70	1.43	1.19	0.96	0.95	2.44	1.56	0.94
Random Forest	0.34	0.41	0.65	0.99	0.91	2.02	1.42	0.95
BRRF	0.27	0.21	0.46	0.99	0.78	1.48	1.23	0.96
BGRF	0.88	1.57	1.20	0.97	1.14	2.36	1.56	0.94

Figure 14. UCS prediction with RF (a) training and (b) testing.

Figure 15. UCS prediction with BRRF (a) training and (b) testing.

Figure 16. UCS prediction with BGRF (a) training (b) testing

Figure 17. UCS prediction with KNN (a) training and (b) testing.

Figure 18. Performance (MAE) comparison of the models.

Figure 19. Variable factor importance for the RF regression model.

Mozumder RA, Laskar AI. Prediction of unconfined compressive strength of geopolymer stabilized clayey soil using artificial neural network. Comput Geotech. 2015;69:291–300. doi:10.1016/j.compgeo.2015.05.021

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