Skid Resistance of nano silica modified roller compacted rubbercrete for pavement applications: Experimental methods and response surface methodology

Figures & data

Table 1. Chemical compositions and physical properties of cement and fly ash

Oxides composition (%)	Cement	Fly ash
SiO2	20.76	57.06
Al2O3	5.54	20.96
Fe2O3	3.35	4.15
MnO	–	0.033
CaO	61.4	9.79
MgO	2.48	1.75
Na2O	0.19	2.23
K2O	0.78	1.53
TiO2	–	0.68
Loss of ignition	2.2	1.25
Specific gravity	3.15	2.3
Blaine fineness (m^2/kg)	325	290

Figure 1. Combined aggregate gradation.

Figure 2. Relationship between cement content and flexural strength.

Table 2. Summary of constituent materials for RCR

Mixture	Cement (kg/m^3)	Nano silica (kg/m^3)	Filler (kg/m^3)	Fine aggregate (kg/m^3)	Coarse aggregate 19 mm (kg/m^3)	Coarse aggregate 6.3 mm (kg/m^3)	Water (kg/m^3)	Crumb rubber (kg/m^3)
M0C0 N	268.69	0	103.76	1,148.05	415.03	416.85	98.24	0
M10C0 N	268.69	0	103.76	1,033.25	415.03	416.85	98.24	114.89
M10C1 N	268.69	2.69	103.76	1,033.25	415.03	416.85	98.24	114.89
M10C2 N	268.69	5.37	103.76	1,033.25	415.03	416.85	98.24	114.89
M10C3 N	268.69	8.06	103.76	1,033.25	415.03	416.85	98.24	114.89
M20C0 N	268.69	0	103.76	918.44	415.03	416.85	98.24	229.78
M20C1 N	268.69	2.69	103.76	918.44	415.03	416.85	98.24	229.78
M20C2 N	268.69	5.37	103.76	918.44	415.03	416.85	98.24	229.78
M20C3 N	268.69	8.06	103.76	918.44	415.03	416.85	98.24	229.78
M30C0 N	268.69	0	103.76	803.64	415.03	416.85	98.24	344.67
M30C1 N	268.69	2.69	103.76	803.64	415.03	416.85	98.24	344.67
M30C2 N	268.69	5.37	103.76	803.64	415.03	416.85	98.24	344.67
M30C3 N	268.69	8.06	103.76	803.64	415.03	416.85	98.24	344.67

Figure 3. Skid resistance test.

Figure 4. Skid resistance of RCR.

Figure 5. RCR sample with crumb rubber particles projecting above the surface.

Table 3. Recommended minimum skid resistance (based on BPN) (ASTM E303, 1997)

Category	Type of site	Minimum Skid Resistance (surface wet)
A	Difficult sites such as:	65
	(i) Roundabouts
	(ii) Bends with radius less than 150 m on unrestricted roads
B	Motorways, trunk and class 1 roads and heavily trafficked roads in urban areas (carrying more than 200 vehicles per day)	55
C	All other sites	45

Figure 6. Relationship between skid resistance of RCR in wet and dry conditions.

Table 4. Variable combinations and responses

Run	Factors		Responses
	A: Crumb rubber (%)	B: Nano silica (%)	BPN (Wet)	BPN (Dry)
1	30	3	41.2	50
2	20	2	58	68.5
3	10	1	50.2	63
4	20	2	56	69
5	10	2	52.5	66
6	20	2	56.5	69
7	30	1	47.1	55
8	20	2	55.5	67
9	20	1	53.5	65
10	20	3	51.7	61
11	30	2	49.5	58
12	10	3	49.5	62
13	20	2	57	70

Table 5. ANOVA for developed response models

Response	Source	Sum of squares	df	Mean square	F-value	p-value
BPN (wet)	Model	261.23	5	52.25	53.16	<0.0001
	A-Crumb Rubber	34.56	1	34.56	35.16	0.0006
	B-Nano Silica	11.76	1	11.76	11.97	0.0106
	AB	6.76	1	6.76	6.88	0.0343
	A^2	86.61	1	86.61	88.12	<0.0001
	B^2	44.19	1	44.19	44.96	0.0003
	Lack of Fit	3.18	3	1.06	1.15	0.4323
BPN (dry)	Model	434.23	5	86.85	81.49	<0.0001
	A-crumb rubber	130.67	1	130.67	122.61	<0.0001
	B-nano silica	16.67	1	16.67	15.64	0.0055
	AB	4.00	1	4.00	3.75	0.0939
	A^2	103.47	1	103.47	97.09	<0.0001
	B^2	72.42	1	72.42	67.96	<0.0001
	Lack of fit	2.66	3	0.89	0.74	0.5816

Table 6. Models validation

Variables	BPN (wet)	BPN (dry)
R ^2	0.974	0.983
Adjusted R ^2	0.956	0.971
Predicted R ^2	0.859	0.930
Adequate precision	21.826	26.485
Standard deviation	0.99	1.03
Mean	52.17	63.35
Coefficient of variation (%)	1.90	1.63

Figure 7. Normal distribution plots.

Figure 8. Predicted vs. actual plots.

Figure 9. 3D response surface plot.

Figure 10. 2D contour plots.

Table 7. Multi-objective optimization

Variables and responses	Goal	Lower limit	Upper limit	Optimum ratio and predicted response
Crumb rubber (%)	In range	10	30	17.20
Nano Silica (%)	In range	1	3	1.87
BPN (wet condition)	Maximize	41.2	58	56.9
BPN (dry condition)	Maximize	50	70	69.5
Desirability (%)				95.3

Figure 11. Ramp for optimum mixtures.

ASTM E303 . (1997). Standard test method for measuring surface frictional properties using the british pendulum tester . West Conshohocken, PA: ASTM International.

 Google Scholar