The Hydration Mechanism And Affection On Durability Of Waste Powder In Cement-based Materials

Currently, a lot of industrial wastes (such as fly ash, limestone powder, waste glass) cause serious environmental pollution and a waste of resources. There are huge needs of concrete in China. Under the premise of guaranteed performance, to use waste inexpensively (especially industrial waste) as much as possible as concrete admixtures which replace part of the cement in the concrete not only re-use to reduce energy consumption and production costs, but also save resources and reduce environmental pollution, which will become the inevitable trend of sustainable development of the concrete industry.In this paper, in-depth study was carried out about the hydration mechanism and properties of fly ash, limestone powder and glass powder in the cement-based material. The main work and conclusions are presented as follows:To use content, water-cement ratio, curing conditions, age and fineness as condition variables, according to permutations and combinations of molding mortar specimens to explore the impact of macroscopic properties of mortar caused by various waste powder. The results shows that low content of fly ash or limestone powder could cause rapid growth strength during late age of mortars but fly ash and limestone complex can effectively reduce the loss of strength. The strength of mortars doped glass powder increases with age growth and the best content is10%. Raising the fineness of glass powder, reducing water-cement ratio or high temperature curing could increase the activity of glass powder ash and improve the strength.Pastes and mortars made with different mix proportions and different contents of fly ash and limestone powder were soaked in a solution of hydrochloric acid and magnesium composite erosion, where the magnesium content was2%. The changes of pH were tested by pH tester and the strength of specimens were also tested by strength experiments and XRD test method to observe the variation of strength and erosion corrosion products.It is showed that a high content of limestone powder and silica fume in mortar specimens has adverse influence on anti-corrosion compound in late erosion, while fly ash and silica fume can improve the anti-corrosion performance. In the early erosion, for the specimens with more limestone powder, acid erosion dominates and exacerbates decomposition of cementitious materials in internal specimens.Using AMBT, the glass powder is used to replace the standard aggregate to study the ASR expansion ratio of mortar bar under different aggregate replacement rates. When the content is50%, the ASR expansion was the biggest in14d. Specimens were made with the glass powder aggregate and standard aggregate in a1:1ratio to explore the inhibitory effect of ASR reaction of mortar bar under conditions of various glass powder fineness, content, curing temperature and age. XRD and SEM test results were combined to study the mechanism of inhibition of ASR by using glass powder.The heat release rate and quantity in the hydration process of cementitious materials is measured uninterruptedly within72hours, using the ToniCal differential thermal type calorimeter produced by Germany's TONI Technik company. According to the method of chemical kinetics, the hydration kinetics models of cement-based materials containing fly ash, limestone powder and glass powder are established. It is concluded that the hydration reaction mechanism of concrete containing fly ash is similar to that of the ordinary Portland cement. Mixing with limestone powder contributes to the early hydration of cement. When the percentage of the mixed limestone powder increases to50%, the hydration reaction of the composite cementitious material is fierce and the hydration process takes less time. The mix of glass powder accelerates the early hydration rate of cement, and the volcanic ash activity is good.Using mercury and water uptake kinetics analysis to analyze the changement of pore size distribution in cement-based materials with different contents of fly ash, limestone powder or glass powder which show pore size distribution in cement-based materials with fly ash is better than that with limestone powder in early time under standard curing condition. The pore size distribution becomes more uniform with the increasing of fly ash and the decreasing of water cement ratio; Due to the hydrate of limestone powder, the strength of cement-based materials with limestone powder grows higher. In a certain scope of content, harmful pores significantly reduce and the structure becomes more compact with the increasing of glass powder because of the filling effect and pozzolanic effect.Some orthogonal experiments are conducted to discuss the effect of the factors that influence the compressive strength of high performance cement-based materials, such as water-binder ratio, content of fly ash, limestone powder and whether adding silica fume or not. Combined with XRD, SEM and other testing methods, it can be seen that the fly ash has less effect on the compressive strength of ultra-high performance cement-based materials. High temperature steaming inspires the high performance cement-based materials mixed with lime stone powder to participate in hydration in a short period of time, generating stable3CaO· Al2O3·CaCO3·11H2O and3CaO·Al2O3·CaCO3·32H2O. The early accelerating hydration of limestone powder is similar to that of pure Portland cement.The variations of compressive strength of the pastes as well as the mortars are studied under the following conditions:the grinding time of the glass powder is respectively set as0.5h,1h and2h, the water-binder ratio is respectively set as0.16and0.20, and the percentage of mixed materials is respectively set as0%,10%,20%and30%. The results show that when the water-binder ratio is0.16, the compressive strength first increases and then decreases with the increase of the percentage of glass powder. Moreover, the compressive strength increases with the increase of the percentage of glass powder when the water-binder ratio is0.20. In comparison,20%percentage of the mixed materials is the best. When the glass powder is grinded for one hour or more, the volcanic ash effect is good in the high performance cement-based materials. Otherwise, the interspace of the cement hydration products is properly filled and the compressive strength is improved.