Performance of lightweight concrete with silica fume after high temperature

In this study, the effect of silica fume on compressive and splitting tensile strength of lightweight concrete after high temperature was investigated experimentally and statistically. The mixes incorporating 0%, 10%, 20% and 30% silica fumes were prepared. After being heated to temperatures of 200, 400 and 800 °C, respectively, the compressive and splitting tensile strength of lightweight concrete was tested. This article adopts Taguchi approach with an L₁₆ (4⁵) to reduce the numbers of experiment. Two control factors (percentage of silica fume and heating degree) for this study were used. The level of importance of these parameters on compressive and splitting tensile strength was determined by using analysis of variance (ANOVA) method.     

Deep learning model for estimating the mechanical properties of concrete containing silica fume exposed to high temperatures

In this study, the deep learning models for estimating the mechanical properties of concrete containing silica fume subjected to high temperatures were devised. Silica fume was used at concentrations of 0%, 5%, 10%, and 20%. Cube specimens (100 mm × 100 mm × 100 mm) were prepared for testing the compressive strength and ultrasonic pulse velocity. They were cured at 20°C±2°C in a standard cure for 7, 28, and 90 d. After curing, they were subjected to temperatures of 20°C, 200°C, 400°C, 600°C, and 800°C. Two well-known deep learning approaches, i.e., stacked autoencoders and long short-term memory (LSTM) networks, were used for forecasting the compressive strength and ultrasonic pulse velocity of concrete containing silica fume subjected to high temperatures. The forecasting experiments were carried out using MATLAB deep learning and neural network tools, respectively. Various statistical measures were used to validate the prediction performances of both the approaches. This study found that the LSTM network achieved better results than the stacked autoencoders. In addition, this study found that deep learning, which has a very good prediction ability with little experimental data, was a convenient method for civil engineering.     

A combined ultrasound method applied to high performance concrete with silica fume

The use of ultrasonic relative amplitude ratio (RAR) and ultrasonic pulse velocity (UPV) to evaluate the strength of high performance concrete (HPC) with 10%, 20% and 30% silica fume content at water/binder ratios from 0.22 to 0.40 with different curing conditions is presented in this paper. As the composition, maturity, free water content and curing conditions are factors that influence the strength of concrete, their effect on the measured UPV and the RAR are determined. Results show that UPV measurement is less sensitive at high level of strength but has good correlation with the compressive strength of HPC with silica fume, whereas RAR maintain good sensitivity at all level of strength (irrespective of the factors that influence the strength) with reduced correlation coefficient. The suggested combined UPV and RAR-strength correlation can be used to estimate the compressive strength of HPC with silica fume and can be combined with other nondestructive testing methods for better estimation of strength.     

硅粉对混凝土高温后力学性能影响的试验研究

用硅粉替代部分水泥掺入混凝土中,对混凝土试块进行200～ 800℃的高温处理,再对冷却后的混凝土试块进行质量损失率测定、超声波检测、抗压强度试验、劈裂抗拉强度试验和微观试验,并对试验结果进行分析和拟合.结果 表明:硅粉会增加混凝土的抗压强度、脆性以及高温爆裂几率,减小高温后混凝土的质量损失率,其最佳掺量为8％,在600...     

超高性能混凝土高温后残余力学性能试验研究

测定了抗压强度高于140MPa的含粗骨料超高性能混凝土和活性粉末混凝土遭受高温作用后的残余抗压强度、残余劈裂抗拉强度和残余断裂能。结果显示,两种超高性能混凝土的残余强度均随着目标温度的升高而呈现先增大再降低的趋势,而残余断裂能均随着目标温度的升高逐渐降低。各目标温度下,含粗骨料超高性能混凝土的残余抗压强度均高于活性粉末混凝土,但其残余劈裂抗拉强度和断裂能低于后者。活性粉末混凝土在300℃临界温度下的峰值残余抗压强度和峰值残余劈裂抗拉强度分别比常温时提高了26.8%和19.3%,800℃高温后的强度损失率分别为72.3%和81.4%。含粗骨料超高性能混凝土在400℃临界温度下的峰值残余抗压强度和在300℃目标温度下的峰值劈裂抗拉强度分别比常温时提高了34.0%和6.8%,800℃高温后的强度损失率分别为70.2%和84.9%。所以,对于有抗火灾高温要求的工程结构,含粗骨料超高性能混凝土适合用于受压构件,而活性粉末混凝土适宜于抗弯构件。     

高性能轻骨料混凝土高温后受压本构关系研究

通过对无纤维全轻混凝土、无纤维次轻混凝土、钢纤维全轻混凝土、钢纤维次轻混凝土进行25、200、400、600、800℃五个温度水平的高温后力学性能试验,研究高温作用对未掺钢纤维和掺入不同体积掺量钢纤维增强轻骨料混凝土力学性能的影响。研究结果表明：随受火温度升高,高性能轻骨料混凝土的强度、弹性模量逐渐下降,立方体抗压强度和弹性模量下降幅度大于轴心抗压强度,纵向峰值应变和横向变形逐渐增大,应力-应变曲线渐趋扁平,上升段线性段比例变小,曲线与横轴包围面积逐渐减小;高性能全轻和次轻混凝土均表现出比普通混凝土更好的抗火性能,但是在高温800℃后,高性能轻骨料混凝土也发生了爆裂,掺入钢纤维后并没能消除爆裂现象,但是减小了高温后试块的表面裂缝宽度;钢纤维改善了高温前后轻骨料混凝土的力学性能,使高温前后轻骨料混凝土的弹性模量和峰值应变均有一定程度的提高。通过回归分析,建立高性能轻骨料混凝土的单轴受压分段应力-应变本构方程,其与试验结果吻合较好。     

无硅灰C80高性能混凝土研究

本文在混凝土理论配合比的基础上，仅改变各掺合料的比例及总掺合料与水泥的比例关系，采用混凝土用中砂配制砂浆，探索了一条以砂浆流动性指导高强高性能混凝土配制的新方法，并应用该方法以290kg/m^3，42．5R普通硅酸盐水泥及粉煤灰、矿渣粉和沸石粉等矿物掺合料配制出28d强度为96MPa的无硅高性能混凝土。     

免振捣自流平高性能轻集料混凝土和高性能轻集料混凝土的研究

本文介绍了国内高性能轻集料的生产状况，指出应加强轻集料混凝土的耐久性研究，应拓宽高性能轻集料混凝土应用的领域；通过试验指出配制免振捣自密实混凝土的可行性，指出开发新掺合料的几个途径。     

硅灰配制海工自密实高性能混凝土的研究

开展了复掺硅灰与矿渣粉海工自密实高性能混凝土的试验研究.试验结果表明,矿渣粉较大的海工自密实混凝土工作性较差,采用硅灰替代矿渣粉可改善海工自密实混凝土的工作性,在复掺硅灰和矿渣粉总掺量为70％,硅灰掺量5％的条件下,掺入55％～65％矿渣粉自密实混凝土具有较高的流动性、填充性、间隙通过性和抗离析性等工作性;28 d抗压强度大于50 MPa,56d的电通量小于1 000C,90d扩散系数小于1.5×10-12 m2/s,具有较高的抗压强度和抗氯盐侵蚀性能,满足海洋环境下抗氯盐侵蚀的质量要求.     

钢纤维混凝土高温应力损伤性能

研究高温对不同钢纤维掺鼍的钢纤维混凝土抗拉、劈拉强度的影响结果,对影响机理进行了简单的分析.试验结果表明:钢纤维混凝土高温后的抗压、劈拉强度随所受最高温的升高而缓慢下降,400℃以后下降稍快.与素混凝土相比,其残余强度率分别可提高30%和20%左右.采用有限元软件ANSYS对混凝土加热过程中的温度场与应力场进行分析,提出了混凝土高温下开裂损伤判据.     

高性能混凝土的抗火灾高温研究进展

本文对目前高性能混凝土的抗火灾高温性能的研究进展进行了总结。高性能混凝土具有良好的力学性能及耐久性能,然而在火灾高温中极易发生破坏成为高性能混凝土广泛应用的绊脚石。通过在混凝土中掺加聚丙烯纤维、钢纤维等提高高性能混凝土的抗火灾高温性能成为学者们研究的热门领域。掺加聚丙烯纤维是防止高性能混凝土发生高温爆裂的有效措施,掺加钢纤维的高性能混凝土可以保持较高的残余力学性能,混掺纤维（钢纤维和聚丙烯纤维）是提高高性能混凝土抗火灾高温性能的良好途径。在高性能混凝土中掺加橡胶粉、引气剂等其他组分是研究高性能混凝土抗火灾高温性能的新思路。     

双掺硅灰、粉煤灰轻骨料混凝土试验研究

基于松散体积法配制同时加入硅灰和粉煤灰两种矿物掺合料的轻骨料混凝土,采用正交试验设计,通过改变净水灰比、粉煤灰掺量、砂率、硅灰掺量四个影响因素,浇筑不同配合比的轻骨料混凝土试块,测定其干表观密度、28 d抗压强度和比强度,分析各影响因素对轻骨料混凝土性能的影响.研究结果表明:硅灰能显著提高轻骨料混凝土抗压强度,且硅灰掺量在3％～6％之间较为合理.并配制出了结构用强度等级为LC30～LC45的双掺硅灰、粉煤灰轻骨料混凝土,为双掺硅灰、粉煤灰轻骨料混凝土的应用提供依据.     

混凝土高温力学性能分析

本文将国内外一些学者对高温后混凝土力学性能的试验进行了分析和对比。探讨了混凝土抗压强度和抗拉强度在不同受热温度下的燹化规律，得出如下结论：抗压强度在300℃前衰减不明显，300℃～800℃是抗压强度衰减的主要温度段，800℃衰减为常温的30％；抗拉强度在300℃前衰减明显，300℃时衰减为常温的50％，800℃时衰减为零。     

高性能轻集料混凝土的研究

采用混合型集料,以堆积６９０ｋｇ／ｍ＾３,筒压强度４．３２ＭＰａ的粘土陶粒,研制出等级为１８００,抗压强度为４０－５０ＭＰａ的轻集料混凝土。该混凝土收缩小,吸水率低,软化系数９４．８５％,经５０次冻融循环无损,耐海水侵蚀,与钢筋粘结力强,可广泛应用于船舶、涵洞、隧道、海港、桥梁及钻井平台等海洋工程,更适用各种轻质高强的工业与民用建筑结构混凝土工程。     

高温对纤维增韧高性能混凝土残余力学性能影响的试验研究

本文通过测定钢纤维、聚丙烯纤维和混杂纤维(聚丙烯纤维和钢纤维)增韧高性能混凝土的高温残余强爱和断裂能，研究聚丙烯纤维、钢纤维和混杂纤维对混凝土高温残余力学性能的影响。实验结果表明，钢纤维和混杂纤维，尤其是钢纤维，显著提高高性能混凝土的残余强度和断裂能。聚丙烯纤维对高性能混凝土残余力学性能的影响很小。     

纤维增强轻骨料混凝土耐高温性能及有限元分析

通过试验研究了轻骨料混凝土的耐高温性能,并与普通混凝土做比较,从残余强度入手,分析高温下混凝土性能的变化规律和机理,并给出了建议的计算公式;用有限元方法对轻骨料混凝土耐高温性能进行分析.结果表明:①统计给出的高温后轻骨料混凝土残余强度曲线的公式与试验结果吻合良好.②全轻骨料混凝土耐高温最好,砂轻骨料混凝土次之,普通骨料...     

多重群体遗传规划在高性能混凝土强度预测中的应用

针对影响高性能混凝土强度的主要因素作为输入因子,28 d抗压强度作为输出变量,应用遗传规划理论(GP)建立了高性能混凝土强度预测的非线性显式数学解析式模型。为了更好地保持进化过程中的遗传多样性,提高求解此问题的效率,提出了多重群体遗传规划理论。通过实测数据进行验证,并分别与线性回归模型和神经网络模型相比较,结果表明,多重群体遗传规划(MGGP)模型具有更高的拟合精度和更好的预测效果,在高性能混凝土强度预测方面有很强的实用价值。     

Compressive strength, chloride diffusivity and pore structure of high performance metakaolin and silica fume concrete

This study is to relate the mechanical and durability properties of high performance metakaolin (MK) and silica fume concretes to their microstructure characteristics. The compressive strength and chloride penetrability of the control and the concretes incorporated with MK or silica fume (SF) at water-to-binder (w/b) ratios of 0.3 and 0.5 are determined. The pore size distribution and porosity of the concretes are also measured. The effect of MK and SF on the interfacial porosity is discussed based on test results. It is found that MK concrete has superior strength development and similar chloride resistance to SF concrete, and the MK concrete at a w/b of 0.3 has a lower porosity and smaller pore sizes than the control (plain) concrete. The resistance of the concretes to chloride ion penetration correlates better with the measured concrete porosity than with the paste porosity. The differences between the measured and calculated concrete porosity is smaller for MK and SF incorporated concrete than for the control concrete, indicating an improvement in the interfacial microstructure with the incorporation of the pozzolanas. This difference is found to be related to the strength and chloride penetrability of concrete to some degree.     

Effect of elevated temperature on the mechanical properties of concrete produced with finely ground pumice and silica fume

This study investigated the effect of elevated temperature on the mechanical and physical properties of concrete specimens obtained by substituting cement with finely ground pumice (FGP) at proportions of 5%, 10%, 15% and 20% by weight. To determine the effect of silica fume (SF) additive on the mechanical and physical properties of concrete containing FGP, SF has been added to all series except for the control specimen, which contained 10% cement by weight instead. The specimens were heated in an electric furnace up to 400, 600 and 800 °C and kept at these temperatures for one hour. After the specimens were cooled in the furnace, ultrasonic pulse velocity (UPV), compressive strength and weight loss values were determined. The results demonstrated that adding the mineral admixtures to concrete decreased both unit weight and compressive strength. Additionally, elevating the temperature above 600 °C affected the compressive strength such that the weight loss of concrete was more pronounced for concrete mixtures containing both FGP and SF. These results were also supported by scanning electron microscope (SEM) studies.     

Interaction between C3A,silica fume and naphthalene sulphonate superplasticiser in high performance concrete

In high performance concrete, fillers and superplasticisers are typically added to the binder system. It is clear that cement, filler and admixture interact, and influence concrete properties. By means of an experimental programme on concrete with different types of Portland cement, with and without partial cement replacement by silica fume, and considering a naphthalene sulphonate superplasticiser, the interaction between C₃A, silica fume and naphthalene sulphonate superplasticiser has been investigated.A higher C₃A content of the Portland cement leads to a higher required dosage of superplasticiser. Partial cement replacement by silica fume leads to an acceleration of the second hydration peak (hydration of C₃S). Early age strength development of the concrete is higher in case of a higher C₃A content.