Influence of type of superplasticizer and cement composition on the adhesive bonding between aged and fresh concrete

The influence of polycondensate and polycarboxylate superplasticizers on the adhesion strength between aged and fresh concrete was investigated by measuring the imbibition of pore solution released from fresh concrete into aged concrete bars and SEM imaging of minerals formed in the transition zone cement/aggregate. Apparently, effective interlocking occurs when much pore solution is soaked up and cement hydrates crystallize abundantly within the transition zone. For the polycondensate, adhesive strength was independent of cement composition while the polycarboxylate only worked with cement possessing high C3A content. The difference is owed to reduced capillary suction behavior of pore solution holding polycarboxylate superplasticizer.