Query: MgO expansion agent

title: Use of MgO expansion agent to compensate concrete shrinkage in jointed reinforced concrete pavement under high altitude environmental conditions
abstract: To mitigate concrete pavement cracking at high altitude locations, jointed reinforced slabs made with concrete containing MgO expansion agent (MEA) were investigated in this study. Firstly, concrete mixtures with varying MEA contents were tested in the lab to evaluate the effect of MEA on concrete's mechanical properties (compressive strength and flexural strength) volume change, and presence of microcracking. Field data including the strain of the concrete slab and the stress of the steel reinforcement in the concrete pavements with and without MEA were collected subsequently at the Shigatse Aiport in Tibet, China. The lab results indicate that the addition of MEA decreases concrete's compressive strength (up to 27% but a slight improvement (up to 12% in flexural strength is achieved when the MEA content is limited to 8% The field study shows that the volume expansion caused by MEA hydration can effectively compensate concrete shrinkage. The concrete expansion could reduce the width of the transverse crack and make concrete slab act like a prestressed member, which could lead to better pavement performance.

title: Early age stability of concrete pavement by using hybrid fiber together with MgO expansion agent in high altitude locality
abstract: Serials of fibers with different elastic modules and MgO expansion agent (MEA) were used to enhance the volume stability of concrete pavement in high altitude localities. Simulation experiments under constant temperature and humidity conditions were carried out to measure early age volume stability of paving concrete by using hybrid fiber and MEA. A test area of concrete pavement was sited to analyses changes of strains inside slabs. The results show that the early age shrinkage of concrete could be effectively compensated by the MEA. However, as the increase addition of hybrid fibers, the expansion of concrete was markedly decreased. Strain records of concrete in test section indicate that the early age volume stability of concrete slabs in high altitude locality could be improved by using hybrid fiber and MEA. Microstructure analysis by scanning electron microscope indicates that the micro cracking inside of concrete was locally restrained by the surrounding hybrid fibers.

title: The effect of curing conditions on the expansion efficiency of MgO expansion agent
abstract: In order to further promote the research and application of MgO expansion agent in concrete field, this paper carried out the effect of different humidity and temperature conditions on the expansion properties of mortar and mortar specimens mixed with MgO expansion agent. In addition, the mechanism of the factors affecting the sensitivity of the MgO expansion agent is revealed by combining microscopic technology. The results show that the higher the curing temperature and the greater the curing humidity, the greater the expansion efficiency of the MgO expansion agent. The temperature of 20~40degC has no obvious effect on the efficiency of the MgO expansion agent, but the expansion value of the specimen doubles as the temperature rises to 40~80degC. Besides, the higher the curing humidity, the better the expansion efficiency of the MgO expansion agent, but the MgO expansion agent is more sensitive to the low humidity environment, and the specimen shrinks in the lower humidity environment (RH=60%

title: Study on limit contents of MgO expansion agent in hydraulic concrete

title: The deformation properties of MgO expansion agent mixed cement paste under different curing conditions
abstract: This paper is concerned with the deformation properties of MgO expansion agent mixed cement paste under different curing conditions.Results showed that with reducing of curing humidity,the effect of compensation shrinkage of cement paste containing MgO expansion agent decreased gradually.While raising the curing temperature,the effect of compensation shrinkage of cement paste containing MgO expansion agent increased,and time needed to obtain stable expansion shortened obviously.

title: Experimental Research on Uusing MgO Expansion Agent Self stressing Concrete filled Steel Tube
abstract: By using high content of MgO expansion agent which produces self stress,the problem of interface disengaging is solved.Experimental research on using MgO expansion agent self stressing concrete filled steel tube is carried out.The experimental results indicate that the characteristic of delayed expansion of MgO expansion agent can ensure the expansive deformation,keep the self stress stable for a long time.MgO expansion agent can produce high value of self stress by restraint of steel tube,and thus enhance the ultimate strength of concrete core subjected to axial compressive loading.Meanwhile,the self stress can further the compaction rate of concrete core.

title: Experimental Research on Using MgO Expansion Agent Self stressing Concrete filled Steel Tube Subjected to Axial Compressive Loading
abstract: Experimental research on using MgO expansion agent self stressing concrete filled steel tube subjected to axial compressive loading is carried out.The effect of initial self stress tube on the ultimate strength and deformation capacity is discussed.The experimental results indicate that the self stress can make concrete core compressed in three directions by restraint of steel tube,enhance the ultimate strength of composite columns subjected to axial compressive loading,delay the expansion of crack of concrete core during elastic plastic stage and increase the tangent elastic modulus of concrete core.Meanwhile,the self stress can make the concrete core more compact and resolve the problem of interface disengaging successfully so that it can ensure the concrete core and steel tube act together in resisting the axial load.

title: MgO expansion agent and its application to mass concrete
abstract: MgO expansion agent is not included in current standard of concrete addition agent in China.Experimental research and engineering practice have proved that concrete has excellent mechanical property and delayed microswelling characteristic when proper amount of MgO expansion agent is added into mass concrete.By making full use of this characteristic,shrinkage distortion of concrete can be counterbalanced and its crack resistance can be improved.As a result,measures of temperature control for mass concrete can be simplified,construction period can be shortened,and project cost can be saved as well.Therefore,it is recommended to list MgO expansion agent into standard of concrete addition agent in China for promoting popularization and application of MgO expansion agent.

title: Effects of CaO based and MgO based expansion agent, curing temperature and restraint degree on pore structure of early age mortar
abstract: High strength and high performance concrete (HSHPC) is prone to cracking at early age due to the large thermal shrinkage and autogenous shrinkage under restraint. CaO based expansion agent (CEA) and MgO based expansion agent (MEA) are widely adopted to compensate for the shrinkage of HSHPC. The macro performance of concrete is closely related to the pore structure. However, there were few researches addressing the pore structure of concrete with the combination use of CEA and MEA. In this study, the effects of CEA and MEA content, curing temperature and restraint degree on the pore structure of early age mortar were investigated by low field nuclear magnetic resonance spectroscopy. The experimental results show that the CEA and MEA addition, curing temperature and restraint degree had a strong influence on the pore structure development of mortar. The most probable pore diameter (MPPD) of mortar with the combination use of MEA and CEA first decreased and then increased with age, differing from the continuous decrease of mortar with CEA addition only. Meanwhile, the MPPD and porosity decreased with age curing at 20 but increased with age curing at 60 In addition, the restraint could improve the pore structure of mortar with CEA and MEA addition. Finally, an analytical bimodal pore structure model was proposed considering the CEA and MEA content, curing temperature and restraint degree. The predicted value of the model shows a good agreement with the present test data.

title: Regulating the Expansion Characteristics of Cementitious Materials Using Blended MgO Type Expansive Agent
abstract: To promote the application of MgO type expansive agents (MEAs) the expansion stresses produced by compacted MEAs with different activities cured in water at 40 degC were measured using a self designed expansion stress test apparatus. Based on these, different MEAs were divided into the early type MgO expansive agent and the late type MgO expansive agent classifications according to the stress curves of compacted MEAs. The two types of MEAs were blended with each other at different ratios and added into cement pastes. Results indicated that the expansion of the cement pastes added with blended MEAs lasted from the beginning to 200 days later, and the expansion characteristics can be regulated by adjusting the blending ratio of MEAs and the choice of types of MEAs. The results suggest that the expansion of MEAs can be improved by using blended MEAs in practical applications.