Effect of Superplasticizer and Wetting Agent on Pavement Properties of Cold Recycled Mixture with Bitumen Emulsion and Cement

Cold recycled mixtures with bitumen emulsion and cement (CRMEC) are an environment-friendly and economic recycling technology in pavement rehabilitation. The low tensile strength and relative low pavement properties of CRMEC greatly limit its application scope. Wetting agent and superplasticizer, which can greatly change the fresh properties of cement bitumen emulsion (CBE) paste and adjust the interaction between bitumen emulsion and cement, were employed to increase the pavement properties of CRMEC. The bulk specific gravity (BSG), indirect tensile strength (ITS), moisture susceptibility, and low-temperature performance of CRMEC were investigated. Results indicate that superplasticizer can greatly improve the BSG, ITS, and low-temperature performance of CRMEC. Besides, CRMEC with superplasticizer has an equal moisture susceptibility as the reference CRMEC. A wetting agent can increase the ITS of CRMEC but decreases its frost resistance and low-temperature deformability. Besides, CRMEC with both surfactants features lower ITS and worse frost resistance and low-temperature performance than CRMEC with only superplasticizer. The corresponding mechanisms were studied. Results indicate that both surfactants can reduce the viscosity of CBE paste. Superplasticizer is beneficial to form a uniform bitumen membrane structure in CBE paste. The wetting agent can greatly decrease the contact angle of bitumen emulsion, but it is harmful to the formation of bitumen membrane in CBE paste. Therefore, superplasticizer is recommended to improve the pavement properties of CRMEC.