研究了在钙溶出作用下,掺和料对28d等强度条件下的海工自密实混凝土(SCC)性能与微观结构的影响.研究结果表明:掺矿物掺和料可以明显延缓SCC在钙溶出作用下的强度损失,并且可以显著改善长时间浸泡时的SCC抗氯离子渗透能力.但是,掺矿物掺和料仅能轻微改善SCC的抗钙离子溶出能力,对改善浸泡早期的抗氯离子渗透能力不利.图像识别技术(Ministarstvo Inostranih Poslova,MIP)分析表明:在钙溶出作用下,硬化水泥浆体主要在1000 nm以下的孔结构中发生明显变化,掺矿物掺和料时,溶出作用对硬化水泥浆体孔结构的影响明显不同,但是均可以明显减小孔结构的劣化作用.扫描式电子显微镜(Scanning Electron Microscope,SEM)分析表明:粉煤灰和矿渣在钙溶出作用下,依然能够保持火山灰和微集料效应,有利于保持C-S-H凝胶形态,可以延缓碱性环境下的劣化作用.

科研团队自主研发出了一种新型高分子溶液型混凝土养护剂X730,通过与两种市售MT和WP养护剂进行试验对比,研究了三种养护剂的有效保水率、憎水性和吸水性等基本性能及其对养护后混凝土强度的影响.结果表明:①采用X730和MT养护剂处理得到的养护膜表面均呈憎水性,而WP养护剂呈亲水性;②三种养护剂均能够有效减小水泥砂浆试件的吸水量与毛细吸水高度,其中X730的防水效果最佳;③采用浸泡法进行养护处理时,X730有效保水率达到80.9％,MT和WP有效保水率分别为62.5％和52.3％;④与水养护相比,采用X730、MT和WP进行浸泡处理的试件,3 d、7 d和28 d的抗压强度均有所下降.但是,X730与MT、WP相比,对混凝土的养护效果最好,28 d抗压强度比达到91.2％,能够满足建材行业标准对养护剂强度比的要求.

综合评述了混凝土搅拌站废弃塑性混凝土再生利用的研究与应用进展,总结了目前国内外对废弃塑性混凝土的再生利用方法,包括用于生产非重要预制构件、自然硬化后生产再生骨料、水洗后砂石分离回收、泥浆水、沉淀或压滤污泥再生利用、废弃塑性混凝土的无水清理与再生利用、添加水化稳定外加剂实现未水化水泥颗粒高效再生利用以及作为预水化水泥基材料抑制超高性能混凝土自收缩等,并提出当前研究与应用存在的问题和今后的发展方向.

The reason for increa.sin.gly serious early-age cracking of current concrete was analyzed.It was indicated that some criterions relating to inhibition of early-age cracking shoud be reappraised.Besides,the control of early-age shrinkage cracking was studied through early-age shrinkage experimentation and it was considered that the key for controlling early-age shrinkage cracking was enhancing early-age humid curing immediately after initial set.

The main portion of shrinkage after 3 days from casting is drying shrinkage.Later, crack occurs stepped-up,for dry shrinkage develops together with load.It is generally considered that drying shrinkage occurs because of the capillary tension as a result of water lost from capillary.Physical graphics and mathematical deduction are displayed,to visually describe the mechanism of dry shrinkage of concrete.

The problems of cracking have been bothering the engineers all the time,even when the technology of concrete makes continuous progress.The early-age cracking is mainly caused by shrinkage.The measures of reducing shrinkage cracking are proposed in the paper based on illuminating the principle to control cracking,including structural measures and material measures.It is expected to be helpful to solve the problem.