废弃新拌混凝土水化休眠与唤醒后再生利用

Hydration Dormancy and Recovery of Waste Fresh Concrete and Recycling

针对商品混凝土搅拌站中废弃新拌混凝土的合理再生利用始终受到凝结时间限制的问题,通过掺加水化抑制剂使废弃新拌混凝土的水化反应延缓至接近停滞,之后在合适的时间掺加水化唤醒剂及附加减水剂使其恢复正常的水化反应速度,然后按照一定的取代率取代新拌混凝土进行再生利用,延长了废弃新拌混凝土的可利用时间窗口,使废弃新拌混凝土再生利用更灵活。通过分析废弃新拌混凝土再生利用结果,得到再生新拌混凝土坍落度、凝结时间和抗压强度的变化规律。结果表明:采取适当休眠措施能使废弃新拌混凝土的可利用时间延长至48 h;如果不使用唤醒措施,经过长休眠的废弃新拌混凝土不能直接使用;在再生利用的过程中,随着取代率的增加,再生新拌混凝土的初凝时间和终凝时间逐渐增加,初凝时间的最大增加幅度为95 min,终凝时间的最大增加幅度为80 min;除了休眠时间12 h、取代率50%和100%以外,其余的坍落度损失要好于基准样;抗压强度有降低趋势,7 d抗压强度比减少了12%~14%,28 d抗压强度比减少了7%~10%,56 d抗压强度比减少了4%~6%。

Aiming at the reasonable recycling of waste fresh concrete in commercial concrete plant being always limited by setting time,the hydration reaction of waste fresh concrete was delayed to near stagnation by adding hydration-inhibitor agent,then to make the hydration of waste fresh concrete return to normal by adding hydration-recovery agent and additional water-reducing agent at appropriate time.After that waste fresh concrete can replace fresh concrete according to a certain replacement ratio to recycling.These measures extended the treatment time of waste fresh concrete and made the recycling of waste fresh concrete more flexible.By analyzing the recycling of waste fresh concrete,the change rules of slump,setting time and compressive strength of recycled fresh concrete were obtained.The results show that the dormancy-recovery treatment of waste fresh concrete can be determined through the study of composite cementitious material paste.Taking proper dormancy measures can extend the treatment time of waste fresh concrete to 48 h.If recovery treatment is not used,the long dormant waste fresh concrete can not be used directly.In the process of recycling,with the increase of replacement ratio,the initial setting time and final setting time of recycled fresh concrete gradually increase,the maximum increase range of initial setting time is 95 min,and the maximum increase range of final setting time is 80 min.In addition to the dormancy time of 12 h,the replacement ratio of 50%and 100%,the slump loss is better than the reference sample.The compressive strength of recycled fresh concrete tends to decrease,the reduction range of 7 d compressive strength is between 12%and 14%,the reduction range of 28 d compressive strength is between 7%and 10%,the reduction range of 56 d compressive strength is between 4%and 6%.