Influences of a New Admixture MX on Concrete Durability

The performance of concrete with a new admi xt ure MX was studied by using the freeze-thaw cycle, permeability and chemical at tack test. The experimental results show that MX improves the durability of conc re te. Within the optimum proportion ranges from 0.1%to 1%,the compressive strength of concrete after freeze-thaw is increased by 20%-50%,and Young's modulus can be increased by 3.76-5.64 times.The strength and weight loss of concrete with 0.4%MX are respectively decreased by 28% and 60% after hydrochloric acid attack. The strength and weight loss of concrete with 0.4% MX are decreased by 5%-20% a fter sulfuric acid and sodium sulfate attack.The permeability of concrete with 1 % MX at 28 days can be decreased by more than 30%. The investigation of the nega tive temperature property of MX and analysis on concrete composition and microst ructure by MIP reveal that the heat conduction is resisted and the freezing proc edure of solution in concrete pore is retarded due to the adding of MX. Moreover ,the pore structure of concrete with MX is improved, thus improving the durabili ty. Based on this study, a resistance model of MX to block the heat and mass tra nsference was proposed, and the mechanism of durability improvement of concrete with MX was explained.

Properties and Microstructure of Marine Concrete with Composite Mineral Admixture

The influences of compositing mineral admixtures on the regularity of mechanical property, workability, durability and microstructure of C50 marine concrete were investigated. The results show that the incorporation of mineral admixtures can improve the mechanical properties and workability of C50 marine concrete, 3 min-doped mineral admixture had excellent resistance to chloride ion permeability. The microscopic structure mixing mineral admixtures system was well-distributed and compact, little macroporeare can be found.

Effect of Alkaline Electrolyzed Water on Performance Improvement of Green Concrete with High Volume of Mineral Admixtures

The strength and durability of concrete will be significantly reduced at high volume of mineral admixture,and the poor early strength of concrete also still needs to be solved.In this investigation,a highly active alkaline electrolyzed waters was used as mixing water to improve the early strength and enhance the durability of green concrete with high volume mineral admixture,the influences of alkaline electrolyzed water(AEW)on hydration activity of mineral admixture and durability of concrete were determined.The results showed that compared with natural tap water,AEW can accelerate early hydration process of cement in concrete and produce comparatively more hydrated products,leading to a 13.6%higher compressive strength than that of ordinary concrete at early age,but the improvement effect of AEW concrete was relatively reduced at long-term age.Meanwhile,the activity of mineral admixtures could be stimulated by AEW to some extent,the strength and durability performance of AEW concrete after double doping 25%slag and 25%fly ash can still reach the level of ordinary cement concrete without mineral admixtures.The SEM micromorphology of 7 d hydrated natural tap water cement paste was observed to be flaky and tabular,but the AEW cement pastes present obvious cluster and granulation phenomenon.The SEM microstructure of AEW concrete with mineral admixtures is more developed and denser than ordinary tap water concrete with mineral admixtures.Therefore,the AEW probably could realize the effective utilization of about 50%mineral admixture amount of concrete without strength loss,the cement production cost and associated CO_(2) emission reduced,which has a good economic and environmental benefit.

Effect of mineral additives and permeability reducing admixtures having different action mechanisms on mechanical and durability performance of cementitious systems

In this paper,the effect of usage of the permeability reducing admixture(PRA)having different action mechanisms on hardened state properties of cementitious systems containing mineral additives is examined.For this aim,three commercial PRAs were used during investigation.The effective parameters in the first and third PRAs were air-entraining and high-rate air-entraining,respectively.The second one contained the insoluble calcium carbonate residue and had a small amount of the air-entraining property.Mortar mixes with binary and ternary cementitious systems were prepared by partially replacing cement with fly ash and metakaolin.The hardened state properties of mortar mixtures such as compressive strength,ultrasonic pulse velocity,water absorption,drying shrinkage and freeze-thaw resistance were investigated.The ternary cement-based mixture having both fly ash and metakaolin was selected as the most successful mineral-additive bearing mix in regard to hardened state properties.In this sense,PRA-B,with both insoluble residues and a small amount of air-entraining properties,showed the best performance among the mixtures containing PRA.The combined use of mineral additive and PRA had a more positive effect on the properties of the mixes.

矿物掺合料对复合胶凝材料浆体静态屈服应力的影响

复合胶凝材料浆体的静态屈服应力可用于表征浆体内部微观结构建立的特性,且对新拌水泥基材料的施工与3D打印过程有很大影响。本文研究了矿物掺合料的种类和掺量对复合胶凝材料浆体静态屈服应力变化规律的影响。研究发现,矿物掺合料的细度增大使颗粒表面的水膜层厚度减小,导致浆体的静态屈服应力增大。复合胶凝材料浆体的静态屈服应力在加水搅拌后的一段时间内缓慢增加,浆体结构建立速率较小。在加水搅拌后大约1.5 h,复合胶凝材料浆体的静态屈服应力迅速增大,表明浆体内部结构的连接程度已接近不可破坏的程度,浆体开始凝结,向固体状态转变。

添加剂对水泥混凝土耐久性能的改善机理研究

旨针对添加剂对水泥混凝土耐久性能的改善机理展开研究,通过分析水泥混凝土的组成和结构特点,以及矿物掺合料、缓凝剂和膨胀剂对水泥混凝土性能的影响,揭示了改善水泥混凝土耐久性的关键因素。分别探讨了矿物掺合料、缓凝剂和膨胀剂对水泥混凝土耐久性能的影响与作用机理,矿物掺合料影响了水泥混凝土的流动性、力学性能、抗渗性、抗冻性和收缩性能;缓凝剂对水泥混凝土的流动性、强度、干缩性能和抗渗性能产生影响;膨胀剂则影响了水泥混凝土的力学性能、抗渗性能、抗碳化性能、抗硫酸盐侵蚀性能以及抗冻融循环性能。

泵送碱式硫酸镁水泥混凝土的制备和性能

碱式硫酸镁水泥混凝土是新开发出来不久的混凝土材料,具有高抗拉强度、抗冲击和耐腐蚀等优点,但由于其较小的塌落度,限制了其工程应用。本文试验研究了不同掺量萘系减水剂对泵送碱式硫酸镁水泥混凝土塌落度和强度的影响,确定强度等级C30、C40、C50和C60的萘系高效减水剂适宜掺量分别为2.0%、1.2%、1.5%和1.8%。分别研究了掺粉煤灰型和矿渣型泵送碱式硫酸镁水泥混凝土基本力学性能及在海水浸泡、淡水浸泡1280 d后的强度保留率并进行机理分析,发现粉煤灰型泵送碱式硫酸镁水泥混凝土抗海水腐蚀性较好,适合东部沿海地区应用;随着海水暴露时间的延长,泵送碱式硫酸镁水泥混凝土的Df值呈现幂函数的降低关系。本文还对大气中暴露2400 d的钢筋泵送碱式硫酸镁水泥混凝土小梁进行观测,未有锈涨现象。本文为碱式硫酸镁水泥混凝土在工程领域的应用具有重大意义。

不同掺合料对喷射钢纤维混凝土性能的影响

依托某重点工程隧道穹顶支护用高性能喷射混凝土的性能要求,配制了C40喷射钢纤维混凝土,研究了掺合料的种类(粉煤灰、专用掺合料、抗裂剂)对喷射钢纤维混凝土工作性、力学性能和耐久性能的影响。结果表明:掺不同掺合料喷射钢纤维混凝土的坍落度均满足(180±20)mm的要求,表观密度稳定在2530 kg/m3左右,抗压强度均满足设计强度等级要求,耐久性能均较好;另外,与掺粉煤灰的喷射钢纤维混凝土相比,掺专用掺合料或抗裂剂的喷射钢纤维混凝土的保水性和黏聚性均较好,力学性能和耐久性能基本均较优,抗渗等级分别达到了P11和P10,28 d碳化深度均小于12.0 mm。

矿渣粉掺合料对C50高性能混凝土综合性能的影响

矿渣粉通常被用作矿物掺合料来制备高性能混凝土,以S95级矿渣粉和C50高性能混凝土为研究对象,评价了不同矿渣粉掺量对C50高性能混凝土综合性能的影响。试验结果表明:随着S95级矿渣粉掺量的不断增大,C50高性能混凝土的抗氯离子渗透性能、抗开裂性能、抗水渗透性能、抗收缩性能、抗冻性能和抗碳化能力均呈现出“先增强后减弱”的趋势,存在一个最佳的掺量使C50高性能混凝土的综合性能达到最佳,在文中所述的试验条件下,推荐S95级矿渣粉的最佳掺量为20%,此时C50高性能混凝土综合性能最佳。研究结果认为,S95级矿渣粉可以用作C50高性能混凝土的掺合料,合适掺量的矿渣粉不但能够有效降低混凝土中水泥的用量,还能有效提高混凝土的综合性能。

大口径PHC管桩混凝土的耐久性试验及工程应用研究

研究了单掺、复掺超细粉煤灰(UFA)、超细矿粉(UMP)、硅灰(SF)对大口径PHC管桩混凝土耐久性的影响,优选出了最佳配合比,并在此基础上,考虑生产经济性,通过优化养护制度,制备了PHC1000AB130管桩。结果表明:当m水泥∶mUMP∶mSF=36∶5∶9、水胶比为0.28时,混凝土耐久性能最佳,其氯离子迁移系数为0.4×10-12 m2/s,280次干湿循环后混凝土抗硫酸盐耐蚀系数为0.85,混凝土抗渗等级达到P20;采用上述配合比生产的PHC1000AB130管桩,施工过程中平均贯入度为0.7~0.8 cm/击,沉桩过程中桩头、桩身均未破损,沉桩效果良好。

易流型大掺量石灰石粉复合掺合料性能研究

针对甘肃平凉地区大量石灰石粉得不到有效利用的问题,本文将当地的石灰石粉和粉煤灰、矿粉、降粘剂等进行复合,制备出满足JG/T 486—2015《混凝土用复合掺合料》中石灰石粉掺量不低于80%的易流型复合掺合料,研究单掺及大掺量石灰石粉复合掺合料对水泥胶砂性能的影响。结果表明:提升石灰石粉的比表面积,可以改善胶砂的流动性,提高其抗压强度,但强度的提高有限;单掺石灰石粉制备的胶砂性能较差,无法满足JG/T 486—2015《混凝土用复合掺合料》的要求和工程需要,建议和其他矿物掺合料复掺使用;三元复合掺合料的性能优于二元复合掺合料,当石灰石粉掺量为掺合料总量的80%,矿粉和降粘剂掺量均为10%时,复合掺合料的性能最佳,SF2石灰石粉复合掺合料的流动度比达到111%、7 d活性指数为71.38%、28 d活性指数为74.71%。

纤维增强碱激发材料的物理力学和耐久性能研究

选择聚丙烯纤维(PP)和玄武岩纤维(BF),采用6种不同体积掺量,制备13组纤维增强碱激发材料(AAC),研究纤维种类和掺量对AAC的工作性能、抗压和抗折强度、抗裂和抗渗性能的影响,并引入纤维增强指数I对各项性能进行探讨。结果表明:相同掺量下PP在改善流动性能方面高于BF,但对抗压强度影响较低,而BF对抗折强度提升率比PP高17.3%;PP在0.5%掺量下可将抗渗等级提高2级,而BF几乎无改善效果。I可同时反映纤维掺量和物理特性,PP的I介于100和350时,其抗折性能、抗压性能均能得到进一步提升,但超过350后对各项性能均产生甚至加剧负面影响;掺加BF的AAC具有更低的阈值。

高浓度搅拌站废浆在混凝土生产中的应用研究

研究了高浓度搅拌站废浆对混凝土性能的影响,考察了掺入不同浓度废浆后溶液pH和密度、混凝土工作性能、力学性能、耐久性能的变化。结果表明,废浆浓度增加,溶液碱度和密度增加;废浆浓度增加会降低混凝土保坍能力,加速混凝土凝结硬化;在废浆掺量30%时,其浓度低于20%则对混凝土抗折和抗压强度影响较小,废浆浓度10%时强度仍有所增长;掺入高浓度废浆混凝土的体积收缩率总体增加,且浓度越高,随龄期收缩越大;较高的废浆浓度会导致混凝土抗碳化和抗氯离子侵蚀能力下降。因此使用高浓度废浆应注意掺量和浓度对混凝土的不利影响。

寒冷地区C60机制砂高性能混凝土配合比研究

寒冷地区因环境较为恶劣,普通混凝土耐久性差,容易出现冻融破坏等问题,严重影响了工程的施工质量和使用寿命,而机制砂高性能混凝土在寒冷地区具有很好的适应性,本文以寒冷地区C60机制砂高性能混凝土为研究对象,通过选取试验材料、优化配合比设计,确定了适用于寒冷地区的C60机制砂高性能混凝土配合比。结果表明:当粉煤灰掺量为20%、硅灰掺量为1.7%时,混凝土整体松软,粘度较低,倒筒时间为3.8 s,粘聚性优异,静置表层无泌浆;当粉煤灰掺量为20%、硅灰掺量为1.7%、矿粉掺量为20%时,混凝土的60 d抗压强度为76.9 MPa,其3、7、28、60 d抗压强度达到设计强度的百分比分别为68.2%、93.7%、118.0%、128.2%;编号GHPB012、GHPB015、GHPB024组混凝土的抗冻等级达到F250。

山西铁尾矿强化即水泥稳定碎石路用性能研究

为使铁尾矿碎石大规模地替代普通石料,需要进一步强化其性能,目前工程中使用较多的石料强化方式为在石料表面喷洒固化剂,以达到表面活化或加固的目的。通过将钠水玻璃、硅烷偶联剂与有机硅树脂3种有机类固化剂对铁尾矿碎石强化后分别测试其物理性能来选择最有效的强化剂,之后选择该强化剂对25%、50%以及75%掺量的铁尾矿进行强化并测试其相应的水泥稳定铁尾矿碎石的耐久性能。结果表明钠水玻璃对铁尾矿的强化效果最好;一般铁尾矿碎石的掺量可以在25%到50%之间,经过钠水玻璃处理后,铁尾矿碎石掺量可以增加到75%;钠水玻璃处理后的铁尾矿碎石混合料的水稳定性、耐冻融、抗冲刷性能均有所提高。

Comprehensive Analysis of the Effects of Superplasticizer Variation on the Workability and Strength of Ready-Mix Concrete

This experimental study aims to examine the influence of many crucial parameters on the workability and compressive strength of Ready-Mix Concrete (RMC). The study utilized two distinct varieties of superplasticizers obtained from the local market. The fine aggregates utilized in this study were sourced from Sylhet sand, whereas the coarse aggregates were comprised of boulder crushed stone chips. The experimental procedures adhered to the requirements outlined by ASTM. A comprehensive investigation was conducted on a range of concrete compositions that used diverse chemical admixtures. The slump test was performed at regular intervals of 15 minutes until the slump value reached or fell below 3 cm after the mixing of the concrete. In the scenario involving two-stage admixture dosage, the second stage of admixture was introduced once the slump reached or dropped below 3 cm, following which the casting process was initiated. The process of curing concrete specimens consists of two distinct stages: the main stage and the final stage. Cylindrical specimens, with a diameter of 4 inches and a height of 8 inches, were manufactured for the purpose of evaluating their compressive strength at both 7 and 28 days. During the experimental trials, the water-cement (w/c) ratio was kept consistent, while different dosages of admixture were applied. The findings of the study indicate that the utilization of a two-stage dose of admixture resulted in enhanced and extended workability, along with higher strength of the concrete in comparison to specimens that did not incorporate any admixture. This research study enhances the comprehension of optimizing qualities of ready-mix concrete (RMC) by varying the superplasticizer, providing useful insights for the building sector.

环渤海湾海洋混凝土结构的长寿命研究与分析

以环渤海湾海洋工程混凝土结构耐久性作为研究对象,根据多年来积累的实验室、海洋暴露站和工程实测数据,采用ChaDuraLife V1.0混凝土结构寿命预测模型与计算机软件,分析不同矿物掺合料掺量、水胶比对海洋混凝土结构服役寿命的影响规律.结果表明:降低水胶比,提高粉煤灰掺量和磨细矿渣掺量都能有效延长海洋混凝土结构的预期服役寿命.以环渤海湾海洋浪溅区混凝土结构为例,最长服役寿命所对应的海洋混凝土配合比最优参数是:粉煤灰和磨细矿渣掺量分别为20%、40%,水胶比为0.30,混凝土结构满足100、200、500 a寿命所需最小保护层厚度分别为60、75、120 mm.

聚羧酸系减水剂掺量和速凝剂掺加时段对无碱液体速凝剂作用效果的影响及机理

本文论述了喷射混凝土工程应用无碱液体速凝剂的重要性,并根据工程应用信息和课题组研究成果,对速凝剂的适应性做了定义,剖析了影响速凝剂应用效果的因素。利用所研制的无碱液体速凝剂AF-LR,以硫酸铝(Al_(2)SO_(4))为主要速凝组分,就聚羧酸系减水剂(PCE)掺量和速凝剂掺加时段对无碱液体速凝剂作用效果的影响及机理进行了试验研究。结果表明:掺加PCE会使AF-LR的速凝作用减弱,原因在于PCE虽可在一定程度上加快浆体水化早期钙矾石(AFt)的生成,但PCE自身具有的缓凝作用却会显著延长水泥水化反应的诱导期;在已拌合好的水泥浆体中,AF-LR掺加时间越晚,促凝效果越差。其原因在于,在没有速凝剂存在的情况下,水泥颗粒与水接触后,水泥水化反应完成诱导前期并进入相对“停滞”的诱导期,铝酸三钙(C_(3)A)的表面被已经形成的AFt紧密包裹,此时加入速凝剂,仅靠速凝剂引入的Al^(3+)和SO_(4)^(2-),难以形成足够多的AFt使水泥浆体快速凝结。

青藏高原地区纤维混凝土抗冻耐久性试验与损伤模型研究

为研究青藏高原环境条件下不同纤维混凝土的抗冻耐久性及冻融损伤演化规律,本研究依托西藏那曲地区某混凝土道路工程,对普通纤维混凝土(NC)、冲磨纤维混凝土(CM)以及膨胀纤维混凝土(PZ)进行了冻融循环试验和相关力学测试,在试验研究的基础上,提出了适用于高原低气压环境下的冻融损伤模型。研究结果表明,从冻融循环试验结果来看,冲磨纤维混凝土(CM)抗冻耐久性最佳,三种纤维混凝土抗冻耐久性排序为CM>NC>PZ。针对本文建立的冻融损伤模型和基于该模型的抗折强度预测方程,采用青藏高原地区某高速工程项目的高寒引气混凝土测试数据进行了验证,冻融后的抗折强度试验值与预测值变化趋势相近且基本吻合。因此,本文建立的青藏高原抗折强度冻融损伤模型是合理且可行的。

不同矿物掺合料对再生抹灰砂浆耐久性能的影响

再生细骨料存在高吸水性及多孔隙的缺点。粉煤灰和砖粉作为矿物掺合料,具有较好的填充效应、活性效应和微集料效应。试验将粉煤灰和砖粉分别掺入到再生抹灰砂浆,研究在不同胶砂比条件下制备再生砂浆的28d收缩率和冻融25次后冻融指标。试验结果表明:掺入适量的粉煤灰和砖粉可以有效改善再生抹灰砂浆的性能,提高其耐久性和工程应用价值。