Study On Shrinkage Property Improvement Of Cementitious Materials With Ground Limestone

Ground limestone is easy-to-get and inexpensive materials, and the grinding energy is low. Ground limestone as admixture added to the cement-based materials can not only improve the performance of cement-based materials but also save energy and reduce emission, reduce the production cost, and disposal cost and lighten environmental load with good technical, economic and ecological benefits. In order to utilize ground limestone scientificly and rationally in concrete and achieve the goal of energy conservation and waste utilisation and improve the performance of cement-based materials, the paper aiming at ground limestone based cementitious material physical and mechanical properties, drying shrinkage and cracking properties are researched. The main content and conclusions are as follows:1. Physical and mechanical properties of cementitious materials with ground limestoneGround limestone can reduce the fluidity of cement paste, but increase the fluidity of mortar; the early strength of hardened paste and mortar appears first increases and then decreases with the increase of ground limestone content. When ground limestone mixed with the content of10%,the strength reaches maximum. The late strength decreasing with the increasing ground limestone content. Water absorption of hardened paste appears a opposite tendency.Fly ash can improve the fluidity of paste with ground limestone and mortar. Double mixed fly ash and ground limestone can improve the fluidity significantly. The early strength of the hardened paste and mortar decreases in a linear with fly ash increasing, the later strength decreases in a quadratic function. When fixed ground limestone or fly ash content, the strength of mortar reduces with an increase ground limestone or fly ash content; When the mortar mixed with ground limestone and fly ash respectively at the content of5%, strength reaches maximum. When ground limestone and fly ash mixed with the total content of20%,30% and40%, strength is lower than the blank group regardless of both the ratio.Calcium sulfate and calcined calcium sulfate have a bad activated effects on the strength of hardened paste with fly ash while sodium sulfate has a good activated effects. Triethanolamine can improve the strength of hardened pastes.Blast furnace slag can reduce the fluidity of the paste with ground limestone, and reduce the early compressive strength, but increase later compressive strength. Silica fume can make the paste with ground limestone fluidity to a sharp decline, but it can improve the early and late strength.The expansive agent can low the fluidity of the paste with ground limestone and compressive strength decreases with the increase of the expansive agent content. Polypropylene fibers and steel fibers can low the fluidity of the mortar with ground limestone. The compressive and flexural strength of mortar increase with the polypropylene fiber content increasing. The compressive strength of steel fiber mortar decreas, but the flexural strength increases when the steel fiber content is increasing.2.Drying shrinkage performance of cementitious materials with ground limestoneThe water loss rate of the paste increases with the ground limestone content increasing. Drying shrinkage value of the hardened paste and mortar shows first increases and then decreases with ground limestone content increasing.The water loss of hardened paste with ground limestone increases with the increasing fly ash/blast furnace slag content, but the impact of ground blast furnace is significantly weaker than the fly ash. Silica fume has little effect. Fly ash improves the drying shrinkage of the ground limestone based harden paste. When ground limestone or fly ash content remains unchanged, drying shrinkage value decreases with its content increasing. When ground limestone and fly ash mixed with respectively at the content of5%,mortar drying shrinkage value reaches the minimum; When ground limestone and fly ash mixed with the total content of20%,30%and40%, its drying shrinkage is lower than the blank group regardless of both the ratio.The drying shrinkage of harden paste with sodium sulfate appears first expansion then shrinkage. Triethanolamine can improve drying shrinkage.Blast furnace slag/silica fume with the replacment of cement increasing can worsen their drying shrinkage performance.The water loss rate of the expansive agent show an increasing trend with the increasing expansive agent content. The specimen show expansion in the water and shrinkage in the dry environment. Strengthening the specimen mixed with expansive agent under water curing condition at early ages can delay the early drying shrinkage. The water loss rate of the mortar appear increase with the content of fiber increasing. Both polypropylene fiber and steel fiber can improve the drying shrinkage of the ground limestone based harden paste.3.The cracking properties of the cementitious materials with ground limestoneThe ground limestone is unfavorable to the cracking properties of mortar when ground limestone content is less than10%while its content is greater than20%can improve the cracking properties of mortar, which the law is accordance with the drying shrinkage. Both fly ash and polypropylene fiber can improve anti-cracking properties of the mortar with ground limestone.4.The application of ground limestone in concreteThe workability of concrete can be improved by double mixed ground limestone and fly ash. When the concrete mixed with the ground limestone or fly ash is less than10%respectively, the design strength requirements of C50is achieved. If the concrete double mixed limestone and fly ash is less than15%, the design strength requirements of C50is also achieved. The drying shrinkage properties of concrete is improved by mixed with fly ash and double mixed with ground limestone and fly ash, which showing a superposition effect. When ground limestone and fly ash mixed with respectively at the content of5%,the strength of concrete reaches maximum and drying shrinkage reaches minimum.