Influence of accelerated curing on the compressive strength of polymer-modified concrete

In recent building practice, rapid construction is one of the principal requisites. Furthermore, in designing concrete structures, compressive strength is the most significant of all parameters. While 3-d and 7-d compressive strength reflects the strengths at early phases, the ultimate strength is paramount. An effort has been made in this study to develop mathematical models for predicting compressive strength of concrete incorporating ethylene vinyl acetate (EVA) at the later phases. Kolmogorov-Smirnov (KS) goodness-of-fit test was used to examine distribution of the data. The compressive strength of EVA-modified concrete was studied by incorporating various concentrations of EVA as an admixture and by testing at ages of 28, 56, 90, 120, 210, and 365 d. An accelerated compressive strength at 3.5 hours was considered as a reference strength on the basis of which all the specified strengths were predicted by means of linear regression fit. Based on the results of KS goodness-of-fit test, it was concluded that KS test statistics value (D) in each case was lower than the critical value 0.521 for a significance level of 0.05, which demonstrated that the data was normally distributed. Based on the results of compressive strength test, it was concluded that the strength of EVA-modified specimens increased at all ages and the optimum dosage of EVA was achieved at 16% concentration. Furthermore, it was concluded that predicted compressive strength values lies within a 6% difference from the actual strength values for all the mixes, which indicates the practicability of the regression equations. This research work may help in understanding the role of EVA as a viable material in polymer-based cement composites.     

Influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of fly ash concrete

This paper presents the results of an experimental investigation carried out to evaluate the influence of Sporoscarcina pasteurii bacteria on the compressive strength and rapid chloride permeability of concrete made without and with fly ash. Cement was replaced with three percentages (10, 20 and 30) with fly ash by weight. Three different cell concentration (0, 10³,10⁵,10⁷ cells/ml) of bacteria were used in making the concrete mixes. Tests were performed for compressive strength, water absorption and rapid chloride permeability at the age of 28 days. Test results indicated that inclusion of S. pasteurii in fly ash concrete enhanced the compressive strength, reduced the porosity and permeability of fly ash concrete. Maximum increase (22%) in compressive strength and four-times reduction in water absorption was observed with 10⁵ cells/ml of bacteria. This improvement in compressive strength was due to deposition on the bacteria cell surfaces within the pores.Calcite deposition in concrete observed nearly eight times reduction in chloride permeability of fly ash concrete. The present work highlights the influence of bacteria on the properties of concrete made with supplementing cementing material such as like fly ash. Usage of bacteria like S. pasteurii improves strength and durability and strength of fly ash concrete through self-healing effect.     

煤矸石生态混凝土透水性与抗压强度研究

本文研究了用煤矸石骨料代替天然骨料配制的透水混凝土的性能,采用正交试验方法分析了主要原材料和配比对煤矸石透水混凝土抗压强度与透水系数的影响,得出了影响强度和透水系数的主要因素是煤矸石骨料的粒径。     

透水混凝土强度和透水性影响因素研究

透水混凝土是一种生态环境友好型混凝土,具有较高的强度和良好的透气、透水性,通过研究不同水灰比、灰集比、胶结材料及集料性能对透水混凝土强度和透水性的影响,为制备性能优良的透水混凝土提供了参考.     

胶粉对砂浆抗折抗压性能的影响

探讨了废旧轮胎胶粉的细度和掺量对水泥砂浆抗折抗压强度的影响。研究结果表明：胶粉的掺入会降低水泥砂浆的抗折抗压强度并随胶粉掺量的加大而减小。在等掺量的条件下,胶粉越细,砂浆的抗折抗压强度越低。     

矿物掺合料对植生混凝土抗压强度及pH值的影响研究

采用矿物掺合料等量取代水泥的方法配制植生混凝土,研究了粉煤灰、硅灰及偏高岭土对混凝土抗压强度和内部孔隙pH值发展的影响规律。研究结果表明:单掺粉煤灰、硅灰及偏高岭土植生混凝土,28 d抗压强度达8.0~10.0 MPa,孔隙率为30%以上,90 d孔溶液pH值降低至11.6~11.8。满足河流护岸、道路护坡等对植生混凝土要求。     

混凝土强度对其动态抗压强度的影响

简述了混凝土建筑材料的性能特点,介绍了不同强度混凝土静、动态单轴压缩试验,通过分析其试验结果,表明混凝土静态抗压强度对其动态抗压强度具有重要影响。     

低温对沙漠砂C25混凝土抗压强度影响

通过设计四因素四水平正交试验,在低温条件下恒温4h,分析粉煤灰掺量、沙漠砂替代率、温度和龄期不同对沙漠砂C25混凝土在低温作用下抗压强度的影响。通过重复正交试验的方差分析及极差分析得出:在-10℃～-40℃条件下,温度对沙漠砂C25混凝土抗压强度有高度显著影响,粉煤灰掺量和龄期对沙漠砂C25混凝土低温下抗压强度有显著影响,沙漠砂替代率对沙漠砂C25混凝土低温下抗压强度影响不显著。     

冻融循环对固化盐渍土的抗压强度与变形的影响

 北方地区冬季结冰与春季融化引起土的冻胀和融沉问题,弱化了土的抗压性能。以研究冻融循环对固化盐渍土抗压性能的影响为目的,完成冻融前后盐渍土、石灰固化盐渍土、石灰+SH固化盐渍土的抗压试验。结果表明：盐渍土、石灰固化土和石灰+SH固化土的抗压强度随冻融次数的增加而减小,石灰+SH固化土的抗压强度均高于另2种土;冻融前后石灰固化土和石灰+SH固化土均为应变软化型,盐渍土则由应变软化型转变为应变硬化型。冻融循环次数相同时,石灰+SH固化土的抗压强度随含水率的增加而减小,其应力–应变曲线逐渐趋于平缓,土的脆性减弱。石灰+SH固化土具有相对较好的抗冻融性能,含水率是影响冻融后土的抗压性能的首要因素。     

Influence of added concrete compressive strength on adhesion to an existing concrete substrate

An experimental study was performed to evaluate the bond strength between two concrete layers of different ages, considering different mixtures of added concrete, with different strengths. The specimens first had the roughness of the substrate surface increased by sand blasting. Later, the new concrete was added. Afterwards, slant shear tests were performed to quantify the bond strength in shear. These tests indicated that increasing the compressive strength of the added concrete relative to the compressive strength of the substrate concrete improves the bond strength and changes the rupture mode from adhesive to monolithic. A finite element analysis showed that, increasing the difference between the compressive strengths of the added concrete and the substrate concrete, higher values of normal stress are present in the interface, for the same level of shear stress. The study presented in this paper reveals that the added concrete, normally with higher compressive strength than the substrate concrete, may possibly have an influence on concrete-to-concrete bond strength. Therefore, design of shear at the interface between concrete cast at different ages, according to Eurocode 2, could be improved, since here only the lowest strength concrete is considered.     

含水率对回弹法检测混凝土强度的影响研究

介绍了用回弹法对不同含水率的混凝土进行强度检测，所得试验数据经二元指数回归分析，提出了含水率对回弹法测强的影响，建立了精度满足要求的回弹法检测潮湿混凝土的强度曲线。     

水灰比对再生混凝土强度影响的试验研究

研究了水灰比对普通与再生骨料混凝土强度的影响。结果表明,混凝土强度与水灰比密切相关。当水灰比大于0.57时,与普通混凝土相类似,再生混凝土的抗压强度随着水灰比的增大而减小;当水灰比小于0.57时,再生混凝土的抗压强度随着水灰比的增大而增大。基准混凝土和再生混凝土超声声速和回弹值随水灰比的变化规律与它们抗压强度值的变化规律基本一致。     

高强混凝土抗压强度的试验研究

随着建筑业的快速发展,混凝土的强度提高是世界各国土木工程界普遍关注的问题。掺有硅灰的混凝土的耐久性得到了研究。研究水胶比和硅灰掺量等参数对高强混凝土的抗压强度的影响.通过试验的方法,找出不同情况下,高强混凝土的最优配合比设计。     

高强混凝土抗压强度尺寸效应综述

尺寸效应是准脆性材料的固有特征.通过对以往110组的HSC抗压强度试验数据的统计分析,得出以15 cm立方体试件抗压强度为基准,对于10 cm立方体试件的尺寸换算系数为0.91;随着基准抗压强度的增大,尺寸效应换算系数略有减小的趋势.混凝土的脆性越大,其尺寸效应越明显.且分析了造成HSC尺寸效应更加明显的原因.     

Influence of dry and wet curing conditions on compressive strength of silica fume concrete

This paper reports a part of an ongoing laboratory investigation in which the compressive strength of silica fume concrete is studied under dry and wet curing conditions. In the study, a total of 48 concretes, including control Portland cement concrete and silica fume concrete, were produced with four different water–cement ratios (0.3, 0.4, 0.5, 0.6), three different cement dosages (350, 400, 450 kg/m³) and three partial silica fume replacement ratios (10%, 15%, 20%). A hyperplastisizer was used in concrete at various quantities to provide and keep a constant workability. Three cubic samples produced from fresh concrete were demoulded after a day; then, they were cured at 20±2 °C with 65% relative humidity (RH), and three other cubic samples were cured at 20±2 °C with 100% RH until the samples were used for compressive strength measurement at 28 days. The comparison was made on the basis of compressive strength between silica fume concrete and control Portland cement concrete. Silica fume concretes were also compared among themselves. The comparisons showed that compressive strength of silica fume concrete cured at 65% RH was influenced more than that of Portland cement concrete. It was found that the compressive strength of silica fume concrete cured at 65% RH was, at average, 13% lower than that of silica fume concrete cured at 100% RH. The increase in the water–cementitious material ratios makes the concrete more sensitive to dry curing conditions. The influence of dry curing conditions on silica fume concrete was marked as the replacement ratio of silica fume increased.     

Influence of corrosion on the ultimate compressive strength of steel plates and stiffened panels

This study concentrates on a comparison between steel plate and stiffened panels subject to localised corrosion. A finite element analysis is used to investigate the effect of random corrosion on the compressive strength capacity of marine structural units. Variables include the extent of corrosion; slenderness ratio and aspect ratio. A corrosion prediction model is incorporated to determine the thickness reduction with time. Corrosion-induced volume loss results in a greater reduction of ultimate strength for slender plates compared to stiffened panels, up to 45%, showing the structural element selection can strongly influence the accuracy of the estimated corrosion damage effect.     

粗骨料类型对混凝土高温后抗压强度的影响研究

对不同骨料类型的混凝土经历不同温度、不同冷却方式后的力学性能进行研究.试验结果表明:高温后不同骨料类型的混凝土立方体抗压强度随着受热温度的升高总体呈下降趋势;不同冷却方式对高温后混凝土立方体的抗压强度有一定影响,并且随静置时间的增加而增加;不同骨料混凝土立方体试块静置后力学性能有较大差异.当温度小于400℃时,硅质骨料...     

催化胶凝剂对大掺量电石渣砖强度的影响

利用自制的催化胶凝剂有效激发电石渣和粉煤灰的活性,从而增加电石渣的掺量,研制出大掺量的电石渣砖。试验结果表明,当掺入50%电石渣,另掺入4%Na2SiO3和1%NaAlO2时,所制得的电石渣砖28 d抗压强度达20.23 MPa,并通过XRD图谱对水化产物和水化机理进行了研究。