| dc.description.abstract | Improvement in the engineering properties of high performance concrete relate not only to strength and durability, but also workability, fluidity and feasibility of adaptation on constructions. Better understanding and control of the dynamic properties of cement during hydration is very important. Slump loss, setting time and hardening rate depend on hydration reaction of cement, and on the establishment of chemical bonds between cement particles.
The workability and the strength development of high performance concrete are highly dependent on the addition of superplasticizer(SP). However, the compositions, properties, and molecular weight for various brands of SP are quite different. The four major components contained in cement have complicate hydration mechanism. The interactions between SP and cement during hydration are not fully understood. This study is to investigate the effects of sulphonated naphthalene formaldehyde condensates (SNF), sulphonated melamine formaldehyde condensates (SMF) and polycarboxylic acid (PCA) SP on the hydration of tricalcium aluminate, tricalcium silicate and cements. Measurements included setting time, heat of hydration, the spread area of mini slump, the flow time of Marsh cone, and the rheological behavior of the pastes. adsorption characteristics of SP on cement particles, ion concentrations in the aqueous phase of cement paste, thermogravimetric analysis, SEM and X ray diffraction analysis, in order to have a better information of the application strategy of every materials.
Test results showed that the adsorption of SP on solid particles resulted in retardation of C3A, C3S and cement hydration, the rate and morphology of hydration products. The setting time and the peak of hydration heat were delayed by the addition of SP. The retarding effect of SP is more apparent along with increasing of dosage. A larger amount of SP was rapidly adsorbed onto C3A compared to that on C3S. The adsorption of SNF and SMF SPs on cement particles was monolayer adsorption. The amount of adsorption was increased with increasing the concentration of SP. When the adsorption has attained saturation, the amount of adsorption was decreased if the concentration of SP was still increased. But, the PCA SPs is Different on adsorption behavior.
The that SNF and SMF SPs are equally effective in making the paste flowable within a few minutes. The PCA SP added paste showed its flowability after 30 minutes of mixing. The flowability of the paste was closely related to the adsorption characteristics of SP on cement particles. A good correlation exists between the results of the minislump test and these of the Marsh cone test. The increase in the spread area of the mini slump test was increased when the flow time was decreased in the Marsh cone test. The Marsh cone test was good for measuring the saturation points of SNF and SMF SPs both of which were 1.2%. It was not suitable for PCA SP. The use of fly ash to replace a portion of cement could reduce the flowability of the paste. However, the flowability was increased when blast furnace slag was used to replace 50% of cement. | en_US |