INFLUENCE OF MINERAL ADMIXTURES ON MECHANICAL PROPERTIES OF HIGH-PERFORMANCE CONCRETE

The improvements of the mechanical properties, including bulk density of fresh mixtures, elastic modulus, and compressive strengths of four high-performance concrete mixtures, made with the addition of fly ash, refined ground blast - furnace microslag (microslag) and silica fume are studied. The concrete mixtures were determined based on the dispersion testing results. The study indicates that the elastic modulus at 28 and 91 days, and compressive strengths of the concretes are improved a lot when fly ash and microslag by 25 percent by weight of cement are added into the mixtures individually. The improvement is especially evident when silica fume by 5 percent and fly ash by 25 percent by weight of cement are added together into the mixture, while the fresh concrete mixture keeps a good workability. Through the analysis of chemically combined water ratios of the four mixtures at various hydration ages, it is found that the addition of all these mineral mixtures are beneficial to the hydration process, especially, at later stages, which might be one of the reasons for the improvement of mechanical properties. (Author abstract) 4 Refs.

Anti-chloride permeability and anti-chloride corrodibility of a green high performance concrete admixture in concrete

The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffusion principle and electro-chemical principle. The GHPC admixture consists of fly ash, gangue, slag, red mud, etc., of which the mass fraction of industrial residues is over 96 %. The anti-permeabilities and anti-corrodibilities of the tested GHPC and normal concrete (NC) are evaluated by the Diffusion Coefficients of chloride which was obtained by measuring the concentration of chloride in the tested systems by the voltage difference method. It is found that the adoption of GHPC admixture greatly improves the anti-chloride permeability and anti-chloride corrodibility by modifying the inner structure and contracting the porosity of concrete to the reduce considerably the diffusion rate of chloride. The admixture is desirable regarding its engineering performances as well as economical and environmental interests.

Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

High-performance concrete （HPC） has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios （mW/mB） in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and cracking of HPC. This study used a shrinkage-reducing admixture （SRA） for that purpose. Concrete was prepared with two different mW/mB （0.22 and 0.40） and four different mass fractions of SRA to binder （w（SRA） = 0%, 1%, 2%, and 4%）. The mineral admixtures used for concrete mixes were： 25% fly ash （FA） and 25% slag by mass of binder for the mixture with mW/mB = 0.40, and 15% silica fume （SF） and 25% FA for the mixture with mW/mB = 0.22. Tests were conducted on 24 prismatic specimens, and shrinkage strains were measured through 120 days of drying. Compressive strength, splitting strength, and static modulus of elasticity were also determined. The results show that the SRA effectively reduces some mechanical properties of HPC. The reductions in compressive strength, splitting tensile strength, and elastic modulus of the concrete were 7%-24%, 9%-19%, and 5%-12%, respectively, after 90 days, compared to concrete mixtures without SRA. SRA can also help reduce drying shrinkage of concrete. The shrinkage strains of HPC with SRA were only as high as 41% of the average free shrinkage of concrete without SRA after 120 days of drying.

The application study of polycarboxylates water-reducing admixture in passenger dedicated line engineering

Polycarboxylate water-reducing admixture possesses the capability which could meet with the comprehensive performance of high performance concrete used in passenger dedicated line engineering.The problems of polycarboxylates water-reducing admixtures existed in the engineering application of were analyzed.At present the key for polycarboxylates application was to settle the compatibility between the water-reducing admixture and the cement and to keep the quality retention of this admixture.

Carbonation Resistance of Sulphoaluminate Cement-based High Performance Concrete

The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete （HPC） were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite （AFt）, decomposes after carbonation.

The Corrosion Fatigue Properties of High Performance Concrete

With the loading test equipment of corrosion fatigue specially designed, the corrosion fatigue characteristics of high performance concrete (HPC) withstanding the interaction of third point fatigue loading and Na_2SO_4 solution were investigated and analyzed. The experimental results indicate that water-binder ratio evidently influences the corrosion fatigue characteristics of HPC, and a moderate quantitative fine mineral admixture enhances the corrosion fatigue resistance of HPC. The effect is more significant when fly ash and silica fume are added.

A Survey of High Performance Concrete Developments in Civil Engineering Field

High Performance concrete (HPC) has received increased attention in the development of infrastructure Viz., Buildings, Industrial Structures, Hydraulic Structures, Bridges and Highways etc. leading to utilization of large quantity of concrete. This paper presents a comprehensive coverage of High Performance concrete developments in civil engineering field. It highlights the High Performance concrete features and requirements over conventional concrete. Furthermore, recent trends with regard to High Performance Concrete development in this area are explored. This paper also includes effect of Mineral and Chemical Admixtures used to improve performance of concrete.

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.

氯盐结晶作用下掺合料对海工HPC性能的影响

通过6 mol/L的NaCl溶液半浸泡和干湿循环实验,对海洋环境氯盐结晶作用进行模拟,研究了氯盐结晶作用下矿物掺合料对海工HPC(高性能混凝土)性能的影响。结果表明:混凝土在氯盐结晶作用下,相对动弹模量和抗压强度后期均呈现下降趋势,其中干湿循环的盐结晶破坏作用最为严重;由于盐溶液毛细上升原因,混凝土在泛霜结晶区也产生明显的氯离子渗透。在28 d等抗压强度下,掺矿物掺合料明显有助于提高混凝土抗盐结晶破坏和抗氯离子渗透性能,其中干湿循环90次后的混凝土,氯离子渗透深度仅约为空白混凝土的2/5。通过微观分析发现,盐结晶破坏主要与混凝土中存在的大孔和毛细孔有关。

基于响应面-蒙特卡罗法的超高性能混凝土性价比研究

目前,学者对于UHPC的研究大多集中在其力学性能方面。本文以UHPC材料的性价比为研究目标,采用响应面-蒙特卡罗法构建响应面函数,并进行随机取样,研究钢纤维掺量对UHPC材料性价比的影响规律。分析了响应面-蒙特卡罗法参数的取值,发现随着钢纤维掺量的增加,UHPC材料的抗拉性价比和抗压性价比均减小。同时,得到了UHPC抗拉性价比和抗压性价比的最佳配比。

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。

冻融循环下掺合料对UHPC强度影响规律研究

为研究冻融循环下掺合料对超高性能混凝土(UHPC)强度的影响,以硅粉(10%、15%、20%)、偏高岭土(5%、10%、15%)、镀铜钢纤维(0.5%、1.0%、1.5%、2.0%)为掺合料,开展冻融前后UHPC抗压和抗折强度试验。建立岭回归模型分析UHPC冻融前后强度变化,并对影响UHPC冻融后强度变化的关键因素进行分析。结果表明:UHPC的强度随硅粉、偏高岭土掺量的增加先增加后减小,随镀铜钢纤维掺量的增加而增大;冻融循环500次后UHPC的抗压和抗折强度均有所下降,抗压强度下降11%~15%,抗折强度下降13%~16%;三种掺料对UHPC强度的影响大小为:镀铜钢纤维>偏高岭土>硅粉。硅粉、偏高岭土、镀铜钢纤维对UHPC强度影响明显。

经济环保型超高性能混凝土力学性能试验研究

为了减少制备超高性能混凝土(Ultra-High Performance Concrete,UHPC)消耗大量水泥造成的CO_(2)高排放,降低施工成本,推广UHPC的应用。研究使用工业副产品作为矿物掺合物部分取代水泥、机制砂或海砂完全取代石英砂在标准养护条件下制备的经济环保型UHPC的力学性能。结果表明:硅灰的掺入提高了UHPC的抗折和抗压强度,当硅灰掺量为30%时,UHPC试件的28 d抗压和抗折强度较基准组分别提高了20.89%和27.30%;粉煤灰和矿粉的掺入均会降低UHPC的抗折和抗压强度;钢纤维的掺入能够显著提高UHPC的强度,掺入2.0%的钢纤维时,UHPC试件的抗折和抗压强度分别提高了9.75%和56.21%;采用机制砂或海砂完全取代石英砂制备的UHPC试件的28 d抗折和抗压强度仅出现略微下降。制备的经济环保型机制砂或海砂UHPC具有良好的力学性能,可应用于工程结构。

不同掺合料对桥面高性能混凝土抗渗性能的影响研究

为探究矿物掺合料对桥面高性能混凝土渗透性能的影响规律,文中对30%粉煤灰、45%矿粉为矿物掺合料的高性能混凝土抗渗性能进行研究。结果表明,粉煤灰的掺入对混凝土早期毛细管吸水率、气体渗透系数、电通量及氯离子扩散系数产生不利影响,但能够改善混凝土后期毛细管吸水率、气体渗透系数、电通量及氯离子扩散系数;同时,对混凝土早期抗渗性能产生正面作用,而对后期抗渗性能产生不利影响。

超高性能水泥基自流平砂浆的试验研究

为了改善传统混凝土面层找平应用砂浆带来施工效率低、自流平效果差、流动性低的缺陷,试验研究超高性能水泥基自流平砂浆。通过水胶比试验确定最优水胶比;外加剂单因素试验研究对砂浆流动度、强度、黏度等影响;多元胶凝材料体系研究对砂浆性能综合影响,并确定最佳配合体系。试验结果表明:(1)适宜水胶比能够使浆体稳定性提高,最佳水胶比0.25,初始流动度146 mm,28 d抗折强度6.64 MPa,28 d抗压强度26.97 MPa。(2)保水增稠剂改善砂浆泌水及提高均匀度,最佳掺量0.65 g时,砂浆黏度值为1 275 m Pa·s;乳胶粉决定拉伸黏结强度,最佳掺量4.5 g时,拉伸黏结强度值达到1.56 MPa。(3)最佳胶凝材料体系为水泥∶矿渣粉∶粉煤灰∶石膏=340 g∶30 g∶30 g∶30 g,流动度更高,强度不减弱,综合性能指标更优。

铁铝酸盐水泥与高性能外加剂在核电工程中的适应性研究

研究了自主研制的高性能外加剂对核电工程铁铝酸盐水泥混凝土性能的影响,通过调整外加剂组分,进行了混凝土工作性、抗压强度测试,优选了适宜核电工程用铁铝酸盐水泥混凝土的最佳外加剂配比。结果表明:通过调整引气剂和消泡剂掺量,可优化混凝土中气泡的稳定性,产生较少连通孔,提高混凝土的施工性能;通过降低减水母液掺量,可解决混凝土的扒底、泌水问题;外加剂中缓凝母液成分优选羟基乙叉二膦酸,最大掺量不宜超过6%;通过降低减水母液和保坍母液掺量,新增降黏母液,可改善混凝土的黏度,降黏母液的最佳掺量为4%;整体来看,高性能外加剂的最优配比为J9组。

生态型超高性能混凝土的研究进展

超高性能混凝土(UHPC)在工作性能、力学性能和耐久性方面表现优异,被认为是混凝土未来发展的重要方向。然而,该材料在环保方面存在一定不足,不利于沙漠周边地区的建设和发展。可以采用工业副产品的矿物掺合料来减少超高性能混凝土中水泥的用量。同时,通过在细骨料中掺入沙漠砂,制作生态型超高性能混凝土,可以有效降低环境的负担。这种改进后的生态型超高性能混凝土在满足工程要求的前提下,更符合环保要求,为沙漠地区和其他地区的建设提供了一种可行的、环保的解决方案。本文主要讨论了矿物掺合料和沙漠砂对超高性能混凝土的影响,提出生态型超高性能混凝土的未来发展。

粉煤灰和矿渣复合掺料对高性能混凝土力学性能和耐久性的影响

本文探究了由粉煤灰和矿渣组成的复合掺料,对高性能混凝土力学性能与耐久性的影响。在试验中,制作了0.47、0.30、0.25三种水灰比的混凝土试件,每种试件下改变复合掺料中粉煤灰与矿渣的比例,验证复合掺料与混凝土抗压强度及干缩率的关系。试验表明,在水灰比较小时,掺入复合掺料代替一部分水泥,可以提高混凝土的后期抗压强度,降低其干缩率;在复合掺料中,当粉煤灰的掺量一定时,矿渣的掺量越多,混凝土的力学性能和耐久性越好。由此可得,在保证混凝土配合比设计合理的前提下,适当掺入粉煤灰和矿渣,减少水泥的用量,能改善混凝土的力学性能,并延长其使用寿命。

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。

复合型掺合料高性能混凝土抗硫酸盐侵蚀性能研究

本文选用乌鲁木齐地区水泥、掺合料、外加剂等原材料,制备不同的高性能混凝土试件,从硫酸盐侵蚀的机理入手,研究掺加复合型掺合料高性能混凝土的抗硫酸盐侵蚀性能。结果表明:当水胶比为0.40或0.35,掺加30%复合型掺合料时,高性能混凝土可以抵抗SO_(2)^(2-)浓度10000mg/L及以下硫酸盐环境水的侵蚀;水胶比≤0.30、掺30%复合型掺合料的高性能混凝土,与水胶比≤0.40、掺50%复合型掺合料的高性能混凝土均能抵抗SO_(4)^(2-)浓度20250mg/L及以下硫酸盐环境水的侵蚀;水胶比和复合型掺合料的掺量均是影响高性能混凝土抗硫酸盐侵蚀性能的重要因素,随着水胶比的降低,高性能混凝土的抗硫酸盐侵蚀能力逐渐增强,而在相同水胶比条件下,随着复合型掺合料掺量的降低,与之相对应的高性能混凝土的抗侵蚀能力随之下降。