Study On The Effect Of Calcium Carbonate Whiskers And Slag On The Shrinkage Performance Of Cementing Cement

In the hardening process of cement slurry, the cement slurry system accompanies with volume changes within the liquid, plastic, solid state. plastic shrinkage of cement slurry can lead to the decrease of the annulus fluid column pressure and form the channeling easily; hardening volume contraction of cement can not only lead to micro gap between interfaces but also lead to the decrease of compressive strength and corrosion proof performances because of the internal shrinkage of cement stone. At present, the use of cement expanding agent is the main method to solve the cement shrinkage, but the common expanding agents have shortages such as premature response time, temperature limit, complex production technology etc. Therefore, it is significant for solving the shrinkage compensation of later stage, overcoming the high temperature limit, reducing the cost and designing high performance cement system to seek special admixture alternative expansion agent and study its physical and chemical properties influence on the cement volume shrinkage.Through the investigation and analysis, calcium carbonate whisker has good stability at high temperature, can improve the micro structure of organic composite materials by filling and the role of a bridge, and it is helpful to reduce the shrinkage of concrete when the specific surface area is smaller than400m2/kg. The principal line of this dissertation is the study of the combination effect of the two materials properties on cement volume contraction. According to the shortcomings of the current evaluation method. OWC-1102high temperature and high pressure cement slurry shrinkage instrument were selected to evaluate cement paste plasticity and volume shrinkage during solidification, comparator was selected to evaluate the external line shrinkage of cement stone and the DKS-III porosity and permeability measurement instrument was selected to evaluate the pore changes caused by internal shrinkage of cement stone. Through90℃and110℃temperature points, five different added amounts, single doped calcium carbonate whisker, slag, complex doped calcium carbonate whisker and slag in the initial and final setting,24hours.48hours,3days.7days,14days,28days age on the volume shrinkage of cement, the cement porosity evaluation of7days,14days,28days age. it studies whether it has the contribution to the volume shrinkage of cement and the optimal dosage and combination, abstracting influence law on cement volume change of the two materials. Finally, it develops project performance evaluation of the optimum dosage cement slurry system.This dissertation studies the influence of calcium carbonate whisker and slag admixture on the performance of cement volume contraction, obtaining conclusions as follow:(1) Single doped calcium carbonate whisker. the contribution of single doped calcium carbonate whisker on cement volume contraction occurs mainly from the final set to28d age. the problems:along with the increase of dosage in plastic and solidification process, it has increased shrinkage of cement paste. The cement sample section of adding calcium carbonate whisker micro cracks are visible.(2) Single doped slag. In the cementing plastic state and solidification process, the shrinkage increases with the decreases of admixture content when the slag content is below15%, the shrinkage increases with the decreases of admixture content when the slag content is over15%. Between solidification and28d age, it can reduce volume shrinkage only when the slag content is more than20%. There is a problem that the same content is hard to juggle the influence on volume contraction. between the periods before and after final set.(3) Mixed calcium carbonate whisker and slag. During cement plasticity process, solidification process and process from solidification to28d age.The volume shrinkage of mixing two materials are less than the single doped with two kinds of materials. It can reduce the microcracking and have more compact structures with adding of cement and slag of calcium carbonate whisker.(4) Influence on porosity. At90℃and110℃, porosity of single doped calcium carbonate whisker, slag, complex doped calcium carbonate whisker and slag in7days,14days,28days are less than the porosity of base formula. The single doped slag has the largest contribution to reducing the cement porosity.(5) The best mix ratio. Through the single doped or doped with two kinds of materials, getting the best adding content:At90℃,5%whisker+5%slag. the volume shrinkage rate is1.3%before the final setting, the inside maximum shrinkage rate is0.308%from solidification to28d age.At110℃,5%of whisker+15%of slag, the volume shrinkage rate is0.3%before the final setting, the inside maximum shrinkage rate is0.007%from solidification to28d age.(6) Project performance. Project performance evaluation results show that:as the conventional density cement slurry with good stability and dispersion, it has good rheology, the thickening curve can form a right angle and thickening time can be adjusted by adding retarder, it has high compressive strength after48hours.(7) The influence mechanism. Ettringite slag reaction reduces the early hydration shrinkage, the filling effect and bridge effect of calcium carbonate whisker, volcano ash effect of slag can reduces the dry shrinkage of cement stone later, compound slag added through the interface to improve the pore structure of whisker and cement paste to reduce the drying shrinkage of purpose.Calcium carbonate whisker was first used in the cement volume contraction study, by adding calcium carbonate whisker, mixed calcium carbonate whisker and slag evaluation experiment, that the basic law of cementing volume shrinkage. The experimental results show that the characteristics of optimization of cement slurry system with low shrinkage and meet the basic engineering properties, with construction potential.