Papers by Author: Xia Chen

Abstract: Upon large demands from southwest of China where a large number of hydropower stations are schemed or under construction with presence of a variety of aggregates, it is of necessity to launch a comprehensive investigation on influence of aggregates on properties of concrete which was rarely reported before. Four types of aggregates selected from different construction sites were used to conduct tests, and results indicated that water absorption of aggregates exhibited a consistent rising tendency over 180 days and it had close relationship with autogenously shrinkage of concrete which varied in the manner that high water absorption of aggregates produced more obvious shrinkage. With employment of advanced temperature and stress machine, concrete made with diorite and basalt was rated better than limestone and natural granite concrete in crack resistance based on comparison of cracking temperature and thermal impact according to RILEM TC119.

Abstract: The computed tomography was introduced to track the development of cracks in cement matrix and interfacial transition zone of MgO concrete under load to failure. Results indicated that some pores were present before concrete was loaded due to none compaction which would tend to initiate cracks expanding. After loading, energy transferring route kept changing and extended towards weak area and it chose to be released through aggregates when concentrated stress on cracks tip surpassed ultimate load with consequences of some cracks getting interconnected with each other through cement matrix. Differentiated and Binarized CT images analysis confirmed that width of cracks was increased and extending routes diversified with loading implemented and interfacial transition zone remained primary choice for cracks development.

Abstract: The computed tomography was introduced to track the development of cracks in cement matrix and Interfacial Transitional Zone (ITZ) of MgO concrete under load to failure and EDS and BEI was employed to investigate the enrichment characteristics of elements in vicinity of ITZ area. Results indicated that cracks intended to extend along boundary of ITZ area which aggravated ITZ as the weak link of concrete structure. The morphology of products of hydration in ITZ area and cement matrix was similar but differed in amount, size and crystal features. Elements Ca, Si, Al and Mg had tendency to enrich in ITZ zone but differed in accumulation extent in orders. MgO was non-uniformly distributed in concrete, fully mixed in construction though, richer in cement matrix than in ITZ, yet MgO later inclined to migrate to ITZ area and the gap in between was mitigated with in-depth hydration.

Abstract: The advanced Temperature and Stress Test Machine was introduced to evaluate the cracking resistance of concrete with inclusion of light-burnt MgO under full restraint by tracking thermal and deformation development. Results showed that light-burnt MgO being incorporated ranging between 4 per cent and 6 per cent by mass of cementitious materials was beneficial to increase the maximum compressive stress and cracking stress of concrete by 0.37MPa and 0.2MPa on average respectively. The maximum temperature was slightly reduced from 59.8°C to 66.2°C while cracking temperature was significantly decreased from 0.8°C to minus 5.6°C. Sensitive anti-cracking coefficient F was forwarded to assess the early cracking tendency of concrete and in general, inclusion of 4 per cent light-burnt MgO with activity of 109s was rated the best in crack resistance.

Abstract: In order to obtain the effect of fibers on fractural property of mass concrete, it had investigated physical performance, elastic modulus and bending toughness of mass concrete with the presence of steel fiber and polypropylene fiber(PPF). Results showed that the inclusion of PPF caused a slight decrease in initial cracking strength, flexural strength and elastic modulus, yet resulted in small increase in equivalent flexural strength, capacity-carrying loading variation coefficient and toughness.The presence of steel fiber was of significance to increase initial-cracking strength, flexural strength and equivalent flexural strength, and produced a slight increase in elastic modulus and significant improvement in capacity-carrying variation coeffecient and flexural toughness. Overall, the inclusion of steel fiber is rated better than PPF in improving ductility and crack resistance of concrete.