| Polycarboxylate superplasticizer(PCE)is a kind of water-reducing agents used widely at present due to their marvelous designabilities in structures,which are able to be developed into a series of products with various properties to meet different demands of construction engineering on the diversities of the concrete.However,the hydration processes of cement can be greatly affected by PCEs’ molecular structures,thereby,resulting in the dissimilarities between the peaceablilities and the early and late strengths of the cement paste.In this dissertation,the PCEs with different densities of carboxylic groups,main chain lengths,side chain structures,side chain lengths and functional groups were designed and synthetised.Different PCEs’ microstructural changes,foaming behaviour and the differences of absorption performance were investigated by their macro-and micro-properties.The different microstructural changes of PCEs were investigated by the means of GPC,DSL and TEM.The results indicated that PCEs would form into associates with different volumes and size distributions in water.Intramolecular association could occur in PCEs,namely one PCE molecular or several PCE moleculars could form into associate.PCE moleculars with short side chains were inclined to distribute into the solution in the form of intermolecular.The increase of the density of carboxylic groups of PCEs’,the extension of side chains and main chains would result in the form of intermolecular association with bigger size.In addition,the size of the intermolecular association mixed with long and short chains was larger than that formed with a single form of side chains.There was little effect of the addition of functional groups and the changes of the ratios(long side chains:short side chains)on the mean diameters in water.The effect of PCE molecular structures on foaming behaviors was examined by measureing of foaming height.The results indicated that with the decrease of densities of carboxylic groups,length of side chains and the amount of AM monomers,the amount of MA and DMC monomers and the foaming height would increase,which could attest to the fact that long side chains,long main chains and high density of carboxylic groups were beneficial for the stability of foams while the addition of functional monomers would lead to low stability.Simultaneously,the moleculars of water-reducing agents with both long and short side chains carried not only on the property of short side chain in good foaming capacity,but also on the property of long side chain in foaming stability.The absorption performance of PCE moleculars with different structures on the surface of cement particles was investigated by TOC,XPS and Zeta potential assays,which indicated that with the increase of the density of carboxylic groups in PCE moleculars,the addition of functional groups,the decrease of the length of side chains and the increase of the amount of short side chains,the absorption capacity of PCE moleculars on the surface of cement paste and the absolute value of zeta potential would gradually magnify.Nevertheless,the absorption capacity would increase at first,subsequently decrease with the extension of the main chains’ length.The moderate length of PCEmoleculars’ main chain(Mw≈130kDa)proved to be maximal in absorption capacity.However,with the decrease of density of carboxylic groups and the length of side chains,the thickness of absorption layer would increase.Overall,the thickness of absorption layer would be maximal when all side chains were short,secondary when all side chains were long while minimal when the ratio of short chains and long chains was 1:1.Besides,the addition of functional groups might result in a slight drop of the thickness.In the last part of this dissertation,the hydration temperature,hydration rate,hydration degree and the change of the heat of hydration during the early period of cement paste mingled with different structural PCE moleculars were assayed by semi-adiabatic calorimeters.On one hand,the results attest to the fact that with the increase of the density of carboxylic groups,the length of main chain and the decrease of the length of short chains,the hydration capacity would be stronger.On another hand,it would help to reduce the heat of hydration and the possibility of temperature cracking if increasing the density of carboxylic groups and shortening the length of short chains.The addition of the PCEs with ester groups could reduce the maximal hydration rate,thereby reducing the partial heat of cement paste.The agglomeration of cement particles,the decrease of contact area between cement and water would occur to prolong the aging of cement by simultaneous absorption of PCEs with long main chains on the surface of several cement particles. |
