Rheological Evaluation of Modified Bitumen by EVA and Crumb Rubber Using RSM Optimization

Table 4

Values of regression coefficients calculated for penetration grade and softening point tests.

Term	Penetration grade				Softening point
	Coef	SE coef	T-value	value	Coef	SE coef	T-value	value
Constant	51.8966	0.3761	137.996	≤0.001	67.069	0.3569	187.905	≤0.001
EVA	−3.6667	0.3698	−9.917	≤0.001	8.5	0.3509	24.221	≤0.001
CR	−3.4167	0	−9.24	≤0.001	4	0.3509	11.398	≤0.001
EVA  EVA	−2.6379	0.3698	−4.84	0.002	−0.7414	0.5172	−1.433	0.195
CR  CR	−0.3879	0.545	−0.712	0.5	0.7586	0.5172	1.467	0.186
EVA  CR	−1.625	0.545	−3.588	0.009	0	0.4298	0	1