Study On Affecting Factors And Forecasting Model Of Coral Concrete Carbonation Depth

Coral concrete has broad application prospects in construction of offshore islands.Researches on the mechanical properties of coral concrete have already been attached importance and made achievements,but the researches on durability are rare.Carbonation is a key factor in the deterioration of concrete structures.This paper studies the following questions:1、The fast carbonation experiments of 11 groups of coral concrete specimens were carried out.Four affecting factors including water-cement ratio,cement content,fly ash content and carbonation age were involved in the experiment.The carbonation age differed from 3 to 28 days,the test points were 3、7、14、28days.The results show that the carbonation depth of coral concrete are positive correlation with water-cement ratio,fly ash content and carbonation age,while negative correlation with the cement content.In order to ensure carbonation resistance of coral concrete,The water cement ratio of coral concrete should not exceed 0.46 and cement content should not be less than 400kg/m³,but we can’t only rely on increasing cement content to reduce carbonation depth of coral concrete.The fly-ash content should not exceed 30%,When the fly-ash content is 15%,carbonation resistance of coral concrete isn’t weakened.Therefore,it is feasible to replace partial cement content with appropriate proportion of fly-ash content.2、Using the orthogonal experimental design method,the effects of multi-factor coupling including water-cement ratio,cement content,environment temperature and relative humidity on the carbonation depth were studied.The range analysis determined optimum mix ratio of coral concrete and the significance of each influencing factor.The results show that the primary and secondary of the influencing factors is cement content,water-cement ratio,relative humidity and environment temperature.The optimal combination is A₁B₁C₁D₃,in other words,when water-cement ratio of coral concrete is 0.3,the cement content is 500kg/m³,environment temperature is 10⁰C and relative humidity is 80%,carbonation depth of coral concrete reach the minimum.Considering environment condition,The results show that the carbonation depth of coral concrete are positive correlation with water-cement ratio and environment temperature,while negative correlation with the cement content and relative humidity.The experimental results are consistent with the single factor test results,and analyze the mechanism of action of various factors.3、a forecast model of coral concrete carbonation depth was established based on double hidden layer BP neural network in MATLAB.The cyclic-training algorithm program was written,and the optimal neurons number of hidden layer was found to be 11 and 5 after 38 cycles nearly million times network training.The minimum root mean square error was 0.67 and the average error was 5.57%.This model is reliable and can be used for forecasting the carbonation depth of coral concrete.