| Coral reefs are a special kind of soil types, the reefs massive structure is formed from coral polyps, tiny animals that live in colonies; when coral polyps die, they leave behind a hard, stony, branching structure made of limestone. According to Chinese Standard JGJ51-2002, coral reefs belong to the natural lightweight aggregate because of its light weight and multi porosity. The ordinary gravel type of coral reefs excavated from the Wei Chau Island of the North Sea in guangxi was used for concrete coarse aggregate, worked out for the apparent density of level1800, compressive strength level of lightweight concrete for CL25. Through the experiment and test analysis, this paper mainly draw the following conclusion:(1) The fatigue test system was used for testing fatigue performance of coral concrete trabecular, and the results showed that the coral concrete trabecular obey logarithmic normal distribution and Weibull distribution, the basic form of fatigue equation was gived, and offer references to project designer in the future. (2) This paper using X-ray diffraction (XRD), scanning electron microscopy, and micro hardness measurement system researched the coral concrete interfacial area mineral composition, mineral morphology and hardness, initially determined the types of mineral composition of interface area and transformation of different mineral composition with different coral concrete age, from the microcosmic view explained the source of the excellent properties of coral concrete. The results show that the contact surface of coral concrete aggregates and cement stone, microhardness far greater than the intensity level of common concrete, the main reason of coral concrete interfacial area hardness’s improvement was attributed to coral aggregate and ordinary Portland cement hydration products of the attapulgite minerals, etc.(3) The main hydration products are CH, AFm, AFt, attapulgite and christobalite in the ITZ. Since the lack of mineral admixtures, the amount of CH crystal seems not obviously decrease along with the cuing ages change. A kind of new mineral product, attapulgite, is generated, its main effect, analogous to C-S-H, can enhance the interface boundary strength. At the same condition, the microhardness values (Hv) of the coral concrete in interface area is significantly higher than the ordinary concrete, and along with the growth of the curing ages, the growth rate of microhardness in the ITZ is faster than ordinary concrete, the existence of attapulgtie crystal may be the primary reason for a better microhardness. (4) At the early period curing ages, attapulgite crystal is needles and fibers, crystals have orientation epiphytic characteristics, were seen forming a continuous film in the direct contact with the aggregate surface. The interface between coral aggregate and cement paste was dense, and the interfacial transition area could not be distinguished easily. At the curing ages of14and28days, there are a lot of hydration products in the ITZ, few voids and holes are found in the ITZ, this phenomenon seems indicated that at the first stage of mixing, the cement paste and water permeated into the surface pores of the coral reefs aggregate, during the period of hydration, hydration products, like CH, S-C-H and attapulgite, are filled in the holes, threrfore, a denser inferface emerged... |
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