Influence Of Spray Process And Maintenance Time After Modification On Mechanical Properties Of Silane Coupling Agent/Granite Interface

Several marco-mechanical experimental researches have indicated that the bond strength of granite/silane coupling agent (SCA)/cement paste interfaces is much higher than that of the granite /cement interfaces. Modification of the aggregates has been done by dipping the aggregates in hydrolyzed SCA solutions for a given length of time. This method, while being appropriate in laboratory, is difficult to be directly used in practice. First, according to current understanding of the working mechanisms of the SCA modification, hydrolyzed SCA would react with the aggregate surface upon dipping of the aggregates into the hydrolyzed SCA solution. That is, the aggregates are not simply taking away a certain amount of the solution. The SCA concentration would be changed after a dipping of the aggregates. It is therefore difficult to control the SCA concentration. Second, dipping would require additional steps in the concrete batching procedure. This will lead to increased time and space requirements. Last, dipping would inevitably cause large amount of residual SCA solution. This will be both a waste of SCA and a threat to the environment. Thus, we try to use atomized SCA to modify the granite/mortar interface can simplify modification process, improve construction quality and save SCA and the environment.In the process of modifying the surface of an inorganic material, the SCA would first be hydrolyzed, causing the alkoxyl group being substituted by OH groups, turning the SCA into silanetriol and releasing alcohol as a byproduct. The OH groups of the triol are reactive. They are ready to condense with other hydroxyl compounds. While in contact with the surface of the material to be modified, the triols condense with the oxide hydrates of the material to be modified. Consequently, chemical bonds are formed between the SCA and the inorganic material. The reactive OH groups of neighboring silanols can also self-condense to produce a polysiloxane layer on the material surface. As can be seen from the working mechanism, the length of the time aggregates are dipped into the SCA solution is a key factor determining the amount of condensed silanols and the reactive OH groups on the aggregate surface. This is therefore necessary to investigate the influence of dipping time upon the bond strength of testing object. To make sure the strength increase is achieved by SCA modification, not by washing the aggregates, contrast tests were also conducted by modifying the aggregates using pure water. In this way, we obtained the optimum modification time. The study shows that three factors affect the SCA modification effects—the existing quantity of active hydroxyl in the SCA hydrolyzed solution, the acidic environmental and the ethanol solution. Results revealed that each factor has different influences at different stages. The strengths of the test specimens reached the maximum if concrete batching was made 24 hours after SCA modification.This paper also presents some preliminary study on combined application of air-entraining agents and SCA. We tried to find reasonable combinations. The tests showed that SCA with negative ionized air-entraining agents exhibited the better effects. But the modification technology still needs the further research.