负温混凝土的力学性能及其影响因素的研究

主要研究了水灰比,矿物掺合料,外加剂及预养制度对负温混凝土抗压强度、抗折强度、轴心抗压强度和静弹性模量的影响。结果表明:负温混凝土-7+28d的各项力学性能的损失率随水灰比的增大而增加。防冻剂和引气剂可以有效地降低混凝土-7+28d的上述各项力学性能损失率,同引气剂相比防冻剂更有效;除抗压强度外,粉煤灰和矿渣对混凝土的-7+28d的各项力学性能不利;经48h预养后所有配合比混凝土的力学性能损失率均显著减小,预养时间对负温混凝土的力学性能的影响要比水灰比、引气剂、防冻剂、矿渣及粉煤灰明显;同其他三种力学性能相比,负温混凝土的轴心抗压强度损失率明显较大。     

特细砂砌筑砂浆7d推定28d抗压强度试验研究

本文通过对不同配比特细砂砌筑砂浆7d和28d抗压强度的试验研究,分析了7d与28d强度的抗压强度的相关关系,得出的关系式对砂浆施工生产和施工中的强度控制以及砂浆配合比调整的辅助设计具有现实指导意义。     

基于性价比优化的混凝土配方设计模型

收集了502组混凝土配方作为训练数据,基于BP神经网络、遗传算法及粒子群算法,构建了一种混凝土配方设计模型,可用于控制混凝土成本和配方优化.所构建的模型考虑了混凝土的原材料成本以及影响混凝土抗压强度的多个关键因素,引入惩罚函数对粒子群算法的目标函数适应度值进行惩罚,解决了混凝土配方设计中非线性约束离散变量问题和连续变量问题,从而达到控制混凝土成本并优化配方的目标.按照构建模型输出27组降低成本后的混凝土配方,并进行抗压强度试验,结果表明：所得配方成本与目标成本的契合度接近97%;降低混凝土单方成本5、10、15元后,所输出的配方均能满足混凝土立方体抗压强度要求.     

Mix proportions for HPC incorporating multi-cementitious composites using artificial neural networks

High performance concrete (HPC) is defined in terms of both strength and durability performance under anticipated environmental conditions. HPC can be manufactured involving up to 10 different ingredients whilst having to consider durability properties in addition to strength. The number of ingredients and the number of properties of HPC, which needs to be considered in its design, are more than those for ordinary concrete. Therefore, it is difficult to predict the mix proportions and other properties of this type of concrete using statistical empirical relationship. An alternative approach is to use an artificial neural network (ANN). Based on the experimentally obtained results, ANN has been used to establish its applicability to the prediction and optimization of mix proportioning for HPC. It was demonstrated that mix proportioning for HPC can be predicted using ANN. However, some trial mixes are necessary for better performance and elimination of material variability factors from place to place. ANN procedure provides guidelines to select appropriate material proportions for required strength and rheology of concrete mixes and will reduce the number of trial mixes.     

废旧橡胶颗粒再生骨料透水混凝土抗压强度和透水性能正交试验研究

废旧橡胶颗粒再生骨料透水混凝土是一种新型绿色环保建筑材料。采用体积法设计再生骨料透水混凝土的配合比,完成9组不同配比28d抗压强度、透水系数及连续孔隙率试验,通过正交试验方法,考察成型锤击次数、废旧橡胶颗粒细度和增强剂掺量对再生骨料透水混凝土抗压强度、透水性能的影响。     

高性能混凝土配合比设计及力学强度试验研究

为提高混凝土的抗压强度和抗冲磨强度,通过不同配合比对普通混凝土进行试验分析。通过试验得出:石粉、灰土和钢渣对混凝土的抗压强度影响并不显著。随着石粉比例的增多,混凝土的抗压强度几乎无明显变化;随着灰土比例的增高,混凝土的抗压强度会出现降低趋势;而随着钢渣比例的增多,混凝土的抗压强度也会出现下降趋势,但影响较小;水灰比对混凝土的抗压强度的变化具有显著性,而砂率和用水量比例则对抗压强度的影响不大。当水灰比逐渐增大时,混凝土的抗压强度逐渐减小;砂率比例逐渐增大时,混凝土的抗压强度无明显变化;用水量比例增多时,混凝土的抗压强度会逐渐上升,但影响较小;石粉、灰土和钢渣对混凝土的抗冲磨强度影响并不显著。随着石粉比例的增加,混凝土抗冲磨强度增大,当石粉比例逐渐增加时,混凝土抗冲磨强度明显增大;随着灰土比例的增多,混凝土的抗冲磨强度减小,并且随着时间的增加,其强度减小趋势便更加明显;随着钢渣比例的增加,混凝土的抗冲磨强度下降,但影响不大。通过试验结果得出最佳混凝土配合比,并通过分析高性能混凝土与混凝土的微观特征得出:普通混凝土内部结构疏松并且有大量的孔洞、分布排列杂乱;而高性能混凝土内部结构较为密集,孔洞较少,高性能混凝土水化后,Ca和Si含量最多,而这两种元素能够形成稳定的结构,因此使得高性能混凝土抗压强度和抗冲磨强度提高。     

Mechanical properties of concrete with recycled coarse aggregate

This paper reports the results of an experimental study on some of the mechanical properties of recycled aggregate concrete (RAC) as compared to those of the conventional normal aggregate concrete (NAC). Ten mixes of concrete with target compressive cube strength ranging from 20 to 50 MPa were cast using normal or recycled coarse aggregates. The development of the cube compressive strength and the indirect shear strength at ages of 1, 3, 7, 14, 28 and 56 days, the compressive strength, the strains at maximum compressive stress and the modulus of elasticity tested by using concrete cylinders at 28 days are reported. The results show that the 28-day cube and cylinder compressive strength, and the indirect shear strength of recycled aggregate concrete were on the average 90% of those of natural aggregate concrete with the same mix proportions. For concrete with cylinder compressive strengths between 25 and 30 MPa, the modulus of elasticity of RAC was only 3% lower than that of NAC. The trends in the development of compressive and shear strength and the strain at peak stress in recycled aggregate concrete were similar to those in natural aggregate concrete.     

免振高性能混凝土力学性能及耐久性研究

采用超细磨粉煤灰和复合高效减水剂双掺技术研制出了Ｃ６０～Ｃ８０免振高性能混凝土,在优选了免振高性能混凝土配合比主要设计参数的基础上,对免振与振捣成型的高性能混凝土的抗压强度、劈裂抗拉强度、抗折强度、弹性模量、抗冻性能、干综性能等进行了对比试验研究。结果表明：免振高性能混缔造人有优异的物理力学性能及耐久性。     

钢纤维再生混凝土在路面工程中的应用研究

本文通过上海市某道路改建工程实例,对含50％再生粗集料的钢纤维混凝土路面进行了较为系统的研究。首先在室内对再生粗集料的密度、洛杉矶磨耗、压碎指标等基本性能进行了测试。然后针对拟定的三组不同配合比的钢纤维再生混凝土试件,在室内进行了抗折强度、抗压强度等试验,最后根据试验结果并结合工程经验,选取了一组较为理想的钢纤维再生混凝土配合比,完成了钢纤维再生混凝土路面的施工。同时对试验路段进行了全面的现场检测,结果证明钢纤雏再生混凝土在普通路面上的应用是安全可行的,而且会有很好的发展前景。     

水泥乳化沥青砂浆强度计算模型

为了建立水泥乳化沥青砂浆（CA砂浆）28d抗压强度计算模型,通过正交试验校验了多种配合比参数对CA砂浆28d抗压强度影响的显著性,通过SEM观察了CA砂浆的微观形貌,分析了配合比参数影响砂浆强度的机理.借鉴混凝土微观力学的理论,建立了基于孔隙率与水化程度的CA砂浆28d抗压强度的理论模型.结果表明：在较大的范围内,该理论模型的计算结果与实测强度有良好的一致性.     

按耐久性设计高性能混凝土的原则和方法

高性能混凝土不是一个混凝土的品种,而是表明混凝土的“性能（performance）或者 质量、状态、水平的一种称谓,是按照具体工程要求和所处环境条件,满足特殊组合的性能而均匀、致密的高质量混凝土。高性能混凝土的耐久性设计步及原材料选择与控制、配合比设计、制备工艺和施工质量控制的全过程。按工程要求的耐久性选定原材料后,从“NEL法的氯离了扩散系数－渗透性关系”中初选水胶比,用绝对体积法计算配合比,进行试配和强度样核。     

含水率对粉煤灰混凝土强度增长的影响研究

通过测试不同配合比、不同含水率的混凝土的抗压强度,研究含水率对混凝土强度发展的影响规律。结果显示,混凝土在28d标准养护后,含水率大的混凝土抗压强度增长较含水率小的混凝土要小。     

双掺粉煤灰和矿渣粉对改性陶粒混凝土性能影响的研究

研究了双掺粉煤灰与矿渣粉对陶粒混凝土和易性及早期强度、后期强度的影响,试验中采用松散体积法对陶粒混凝土的配合比进行设计,以确定最佳配合比,测定了12组不同配合比陶粒混凝土的抗压强度.研究结果表明:对陶粒混凝土进行拌合之前应将陶粒提前预湿6h;随着双掺掺合料比例的增加,双掺掺合料陶粒混凝土的抗压强度也随之增加;45％比例...     

Compressive strength and stability of sustainable self-consolidating concrete containing fly ash,silica fume,and GGBS

This paper presents the findings of an experimental program seeking to understand the effect of mineral admixtures on fresh and hardened properties of sustainable self-consolidating concrete (SCC) mixes where up to 80% of Portland cement was replaced with fly ash, silica fume, or ground granulated blast furnace slag. Compressive strength of SCC mixes was measured after 3, 7, and 28 days of moist curing. It was concluded in this study that increasing the dosage of fly ash increases concrete flow but also decreases segregation resistance. In addition, for the water-to-cement ratio of 0.36 used in this study, it was observed that the compressive strength decreases compared to control mix after 28 days of curing when cement was partially replaced by 10%, 30%, and 40%of fly ash. However, a fly ash replacement ratio of 20% increased the compressive strength by a small margin compared to the control mix. Replacing cement with silica fume at 5%, 10%, 15%, and 20% was found to increase compressive strength of SCC mixes compared to the control mix. However, the highest 28 day compressive strength of 95.3 MPa occurred with SCC mixes in which 15% of the cement was replaced with silica fume.     

土壤固化剂稳定粉质黏土性能的试验研究

以河南省境内某段高速公路附近的粉质黏土为原材料,通过室内试验,首先对比了掺或不掺固化剂的情况下,水泥质量分数分别为5%,10%,15%和20%时集合料的7 d无侧限抗压强度,结果表明掺固化剂能明显提高集合料的无侧限抗压强度;其次制备了不同配合比的集合料试件,分析了水泥和固化剂含量对集合料最大干密度、最佳含水量、7 d和28 d无侧抗压强度2、8 d间接抗拉强度的影响,综合试验结果与成本等因素,选定了最优配合比为m(水泥)∶m(固化剂)∶m(粉质黏土)=4∶8∶88;最后,对该最优配合比进行了延迟和干缩等路用性能试验及SEM微观分析,并在某高速公路选取100 m的底基层进行了现场试验和追踪调查,结果表明上述最优配合比集合料完整密实且强度较高,未出现病害,路用性能较好.     

Multiple linear regression,artificial neural network,and fuzzy logic prediction of 28 days compressive strength of concrete

Evaluating the in situ concrete compressive strength by means of cores cut from hardened concrete is acknowledged as the most ordinary method, however, it is very difficult to predict the compressive strength of concrete since it is affected by many factors such as different mix designs, methods of mixing, curing conditions, compaction, etc. In this paper, considering the experimental results, three different models of multiple linear regression model (MLR), artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) are established, trained, and tested within the Matlab programming environment for predicting the 28 days compressive strength of concrete with 173 different mix designs. Finally, these three models are compared with each other and resulted in the fact that ANN and ANFIS models enables us to reliably evaluate the compressive strength of concrete with different mix designs, however, multiple linear regression model is not feasible enough in this area because of nonlinear relationship between the concrete mix parameters. Finally, the sensitivity analysis (SA) for two different sets of parameters on the concrete compressive strength prediction are carried out.     

机制砂与细砂高性能混凝土和易性与抗压强度的研究

本文研究了机制砂和细砂的比例对混凝土和易性和抗压强度的影响。试验结果表明:在水泥掺量一定且机制砂和细砂的比例为1∶1时,混凝土的和易性良好、抗压强度最高;机制砂与细砂配制的混凝土7天强度增长较大,14天到28天强度增长缓慢。SEM形貌图及EDS能谱表明,龄期为14天的混凝土已经有大量的C-S-H生成,且密实性良好,与28天相比,密实性无明显区别。     

Factors affecting the strength and creep properties of laterized concrete

Many factors are known to affect the strength and creep properties of laterized concrete prisms. Those considered in this report include: mix proportion, water/cement ratio, curing ages, grain size ranges, stress level, lateritic soils-river sand variation. Moulds of 50 × 50 × 250 mm high were used for making prism specimens. Four different mix proportions were selected while prism specimens were cast using four different water/cement ratios which were kept constant for each mix proportion. Prism specimen were also made using a constant water/cement ratio with different river sand lateritic soils proportions forming the fine aggregate component of the selected 1:2:4 mix proportion. The results have shown that increase in cement content and decrease in water/cement ratio of laterized concrete prisms bring about increase in the compressive strength obtained. The mix ratio of 1 part lateritic soils plus $\text{1}\text{1}\text{2}$ parts river sand produced a slightly higher strength than the conventional concrete grade 20. There is also a corresponding increase in the creep of laterized concrete prisms due to different curing ages and different imposed loads. Both the mix proportion and the grain size ranges affect the creep of laterized concrete prisms differently. Unlike the creep of concrete which shows some definite recovery after unloading, laterized concrete prisms did not show any form of recovery, and there was drastic reduction in the compressive strength of the specimens after unloading.     

基于孔隙率控制的多孔混凝土配合比设计方法

对基于孔隙率控制的多孔混凝土配合比设计方法展开研究,结合配合比试验阐述配合比设计的过程和要点,表明这种方法较为简便、实用,可有效地实施对多孔混凝土综合性能的调控。通过对抗压强度、孔隙率、水胶比的相互影响进行分析和对比表明:对多孔混凝土而言,孔隙率对抗压强度的影响较为显著,而水胶比对抗压强度的影响较小。通过对孔隙率的比较,分析因振捣成型方法造成孔隙率产生偏差的原因,并针对减小孔隙率偏差的措施提出了建议。     

Prediction of compressive strength of SCC and HPC with high volume fly ash using ANN

An artificial neural network (ANN) is presented to predict a 28-day compressive strength of a normal and high strength self compacting concrete (SCC) and high performance concrete (HPC) with high volume fly ash. The ANN is trained by the data available in literature on normal volume fly ash because data on SCC with high volume fly ash is not available in sufficient quantity. Further, while predicting the strength of HPC the same data meant for SCC has been used to train in order to economise on computational effort. The compressive strengths of SCC and HPC as well as slump flow of SCC estimated by the proposed neural network are validated by experimental results.