Research Of Relationship Between Micro Structure And Properties For Self-leveling Mortar

Ⅰ In this paper, the influence of components of ternary system of Portland cement-aluminatecement-anhydrite on the performance of self-leveling mortar is studied, and the relationship between theperformance and its microscopic structure is analysised. The resout shows that it is a very complex system.In such a system, the components are of an extremely accurate mixture ratio accordingly, and theperformance is very sensitive to the different mixture ratios. This kind of complex relationship reflects inthe following aspects:1. In liquidity, with the increase of mixing amount of anhydrite, only in a certain range, it hasinsignificant influence on mortar water; if beyond this range, with the increase of mixing ratio of anhydrite,mortar water consumption increases. The water with aluminum acid salt mortar cement mixed quantityincreases. The motor water consumption increases with the mixting amount of aluminate cement.2. The ternary system of Portland cement-Aluminate cement-anhydrite, hydration reactions of eachcomponent are not independent, but interactive. In such a system, no matter the hydration processes orhydration products they may be different to that when each component remains separate, and have a closerelationship with the mixture ratio. This relationship does not simply add all the influences together, butinteracts and impacts on each other.3. In the ternary system of Portland cement-Aluminate cement-anhydrite, each component's impacton the performance is not independent, but interactive. In such a system, a component's impact on theperformance may interact with the quantities of other components. This interaction does not onlyrepresent in quantitative changes, but also in qualitative changes.Ⅱ Through the analysis of variance and hierarchical analysis method, this paper studies the complexrelations in this system to achieve the best proportionate relationship. Using the X-RD, thermal analysisand other methods, the paper researches into mechanism of the interactions of various components, andpoints out that the root causes of the complicated relationship are as follows:1. In the ternary system of Portland cement-Aluminate cement-Anhydrite, different hydrationproducts have quite different properties. In this system, there may be many hydration products, such as C-S-H gel, Ca(OH)2, ettringite, alumina gel, C3AH6, dihydrate gypsum, and those hydration productsperformance are different. For example: C-S-H gel contributes a lot to the strength, but will lead to alarger shrinkage deformation; while ettringite contributes to the early strength, it will make cement stoneexpanse; the generation of alumina gel is useful to fill the hole, however, it increases the shrinkagedeformation; C3AH6and dihydrate gypsum have a low strength. Due to the different performances of thehydration products, the types and quantities changes of hydration products will lead to the performancechanges greatly.2. Ettringite's formation and quantity depends on the proportional relationship of aluminate cementand anhydrite, as well as the liquid phase alkalinity. hydration products of aluminate cement depend onwhether there is any anhydrite or not. When no anhydrite exists, the hydration products are C3AH6andalumina gel; when anhydrite exists, the hydration products are ettringite and AFm. And when andydrite ismore than enough, dihydrate gypsum will turn up.3. The proportional relationship of aluminate cement and Portland cement controls the quantities ofalumina gel and C3AH6. The main mineral composition of aluminate cement is low-calcium calciumaluminate, which will absorb Ca(OH)2to generate C3AH6, and when the Ca(OH)2is insufficient, it formalumina gel. In this system, Ca(OH)2comes from Portland cement. Thus it is concluded that theproportional relationship of aluminate cement and Portland cement determines sufficiency or insufficiencyof Ca(OH)2, therefore, it also determines the quantities of alumina gel and C3AH6.In this system, the performance is very sensitive to the physical structure, and the physical structureis also sensitive to the compositions. Therefore, the fluctuation of compositions can cause the significantchanges in performance, or even a qualitative leap.Ⅲ This paper also studies the function and mechanism of fly ash in different systems, the studyshows that:1．In Portland cement, when only mix with fly ash, the amount hydration product of Portlandcement in the system will decrease, thus the strength of hardening mortar will decrease while the amount offly ash increases, and at the same time as the microaggregate, fly ash also limits the dry shrinkagedeformation of the hardened cement paste.2．In the Portland cement-Aluminate cement system, aluminate cement and fly ash absort Ca(OH)2 at the same time, due to this kind of competition, it leads to insufficient of Ca in the system, thuspozzolanic reaction of fly ash is hard to continue. Under this circumstance, while increasing the amount offly ash, hardening the strength of the mortar significantly gets lower, and dry shrinkage deformationreduces gradually.3．In the system of Portland cement-Anhydrite, when mixing with fly ash, anhydrite acts as aexcitant to boost the generation of anhydrite, however, it cannot change the tendency of reduction on thestrength and dry shrinkage deformation, and only has some moderating influence on the tendency ofreduction.4．In the system of Portland cement-Aluminate cement-Anhydrite, when mixing with fly ash,Ca(OH)₂becomes less, and alkalinity gets lower, which go against the generation of ettringite. Because Cais insufficient, the pozzolanic reaction of fly ash is hard to proceed, therefore, with the increasing of flyash, the strength and the dry shrinkage deformation of hardened mortar decrease gradually, and thehygroscopic coefficient&rate increase gradually.