Quantitative Determination Of Mineral Admixtures In Fresh Cement Mortars And Concretes

In recent years, with the reapid development of construction industries, mineraladmixtures, such as fly ash, granulated blast furnace slag, silica fume, limestonepower, etc, are being widely used to replace cement or aggregates in concrete. Theycan not only reduce the heat of hydration, improve the rheological properties andenhance the durability of concrete, but can also reduce the cost of concrete andfacilitate the sustainable development of construction industry. However, in order tomake the cementitious materials to achieve performance expected, flyash/slag/limestone power and cement must be in the appropriate proportion. To avoidmaking adverse impact on concrete because mineral admixtures were unreasonablymixed in concrete, it is very important to determine the mineral admixture content soto ensure the correct addition of mineral admixture in cement and concrete, toguarantee the quality of concrete materials and structures.At present, no publication has been identified about the quantitativedetermination of fly ash, slag and limestone power in fresh cement mortar andconcrete containing several mineral admixtures, and as to how to quickly andaccurately determine water-binder ratio is also the problem of engineering to be face.Therefore, this thesis is focused on the determination of several mineral admixtures offresh cement mortar and concrete and the determination of water-binder ratio in freshconcrete.Based on GB/12960-2007for quantitative measurement of mineral admixtures incement, a method was developed for determination of mineral composition of ternarycementitious system mixed in fly ash and slag. The effects of several factors, such asthe hydration time、80μm-residue of fly ash on sieve、silt content of fine and coarseaggregates and water-reducing agent on the measurement were studied.The resultsshows that, during the first3hours, the hydration time did not show effect onmeasurement results, but the residues of fly ash on80um sieve and silt contents ofaggregates demonstrated significant effect on the measured results. There was a goodlinear correlation between measured and actual contents of mineral admixtures infresh cement mortar and concrete after the consideration of residue and silt in thedeveloped method this paper.Based on the work principle of differential thermal analyzer and the latestresearch of the quantitative determination of mineral admixtures in fresh mortar and concrete above, a method was developed for determination of mineral composition ofquaternary cementitious system mixed fly ash, slag and limestone power. Afterstudying the samples’ weightlessness arise from the decomposition of limestonebetween600~900℃was analysis and considering the influence of residue contentof fly ash on an80-um sieve, silt content of aggregates, and combining with theselective solution method of GB/T12960-2007, the measurement formulas werededuced and the method was developed for determination of mineral composition ofquaternary cementitious system. With the developed methods to determine the mineralcomposition in fresh cement paste, mortar and concrete, the deviations between themeasure value and the actual content of mineral mixture of cementitious system arewithin3%.For the determination of water-binder ratio in fresh concrete, because sampling isnonuniform and the separation of aggregates and cementitious is incomplete, and theinfluence of silts of sand and gravel, the relative errors of measured value and actualvalue of water-binder ratio is between-11.2%~6.4%, therefore the methodcombining microwave method and the sieving method proposed by this paper todetermine water-binder ratio is not apply currently.