Relationship between ultrasonic velocity and compressive strength for high-volume mineral-admixtured concrete

Ultrasound is used to evaluate the compressive strength of concrete with mineral admixtures. In addition, the relationship between ultrasound velocity and compressive strength of concrete are evaluated. High-volume fly ash (FA), blast furnace slag (BFS) and FA+BFS are used as the mineral admixtures in replacement of Portland cement (PC).

Compressive strength and ultrasonic pulse velocity (UPV) were determined at the 3-, 7-, 28- and 120-day curing period. Both compressive strength and UPV were very low for all the levels of mineral admixtures at an early age of curing, especially for samples containing FA. However, with the increase of curing period, both compressive strength and UPV of all the samples increased. The relationship between UPV and compressive strength was exponential for FA, BFS and FA+BFS. However, constants were different for each mineral admixture and each level replacement of PC.     

Physico-chemical interaction between mineral admixtures and OPC–calcium sulfoaluminate (CSA) cements and its influence on early-age expansion

The present study aims at examining the physico-chemical factors influencing the expansion characteristics of OPC–CSA blend in the presence of mineral admixtures. Three different admixtures: Class ‘F’ fly ash (‘F’FA), Class ‘C’ fly ash (‘C’FA) and silica fume (SF) were used as 15%, 15% and 5% replacement of total cementitious binder. Longitudinal expansion of cement pastes prepared at w/cm – 0.44 showed that the Class ‘F’FA increased the expansion whereas the Class ‘C’FA and SF reduced the expansion. The pore solution of the OPC–CSA cement pastes was extracted at different ages to monitor the concentration of various ionic species. The saturation level of ettringite was determined using a geochemical modeling program (GEMS). Furthermore, an upper bound of crystallization stress was estimated. The expansion behavior in the presence of Class ‘F’FA and SF was found to be influenced by the changes in the stiffness, whereas the expansion of the Class ‘C’FA-based mixture was governed by faster hydration of ye'elimite.     

Formulating a low-alkalinity, high-resistance and low-heat concrete for radioactive waste repositories

Investigations were carried out in order to formulate and characterize low-alkalinity and low-heat cements which would be compatible with an underground waste repository environment. Several systems comprising Ordinary Portland Cement (OPC), a fast-reacting pozzolan (silica fume (SF) or metakaolin (MK)) and, in some cases, a slow-reacting product (fly ash (FA) or blastfurnace slag (BFS)) were compared. Promising results were obtained with some binary mixtures of OPC and SF, and with some ternary blends of OPC, SF and FA or BFS: pH of water in equilibrium with the fully hydrated cements dropped below 11. Dependence of the properties of standard mortars on the high contents of FA and SF in the low-pH blends was examined. Combining SF and FA seemed attractive since SF compensated for the low reactivity of FA, while FA allowed to reduce the water demand, and dimensional variations of the mortars. Finally, low-heat (ΔT < 20 °C under semi-adiabatic conditions) and high strength (≈ 70–80 MPa) concretes were prepared from two low-pH cements: a binary blend made from 60% of OPC and 40% of SF, and a ternary blend including 37.5% OPC, 32.5% SF and 30% FA.     

粉煤灰海工高性能混凝土的应用研究

针对粒化高炉矿渣粉和硅灰存在的缺陷。研究采用粉煤灰替代粒化高炉矿渣粉配制混凝土,进而观察其力学性能、抗氯离子渗透性以及胶凝材料的水化热。研究结果表明,所配制的混凝土能满足海工高性能混凝土高耐久性的需要,粉煤灰替代粒化高炉矿渣粉胶凝材料具有较低的水化热,有利于大体积混凝土的施工。     

磨细矿物掺合料对水泥硬化浆体孔结构及砂浆强度的影响

采用压汞法研究了钢渣、矿渣、粉煤灰单掺或复掺对水泥硬化浆体孔结构的影响.同时还研究了掺合料单掺或复掺对水泥砂浆抗压强度的影响.结果表明:掺合料单掺或复掺对早期水泥硬化浆体的孔结构有一定的劣化作用;水化后期,矿渣与钢渣均明显降低了水泥硬化浆体的孔隙率,矿渣与粉煤灰均明显降低了水泥硬化浆体的中值孔径并改善了水泥石的孔径分布,掺合料复掺对改善水泥硬化浆体的孔结构有积极作用,尤其是掺合料三元复合可取得最佳的效果.3种掺合料降低水泥硬化浆体孔隙率能力的大小顺序为:矿渣>钢渣>粉煤灰.3种掺合料降低水泥硬化浆体孔径并改善孔径分布能力的大小顺序为:矿渣>粉煤灰>钢渣.掺合料降低了水泥砂浆早期的抗压强度,却增加了水泥砂浆90 d的抗压强度.掺合料的活性大小顺序为:矿渣>钢渣>粉煤灰.     

矿物掺合料混凝土碳化性能试验研究

通过快速碳化试验,综合考虑水胶比、掺合料种类、掺量等因素,对掺合料混凝土碳化规律进行了研究.结果表明:低水胶比是保证掺合料混凝十具有较高抗碳化能力的重要手段之一.掺合料总掺量相同时,掺合料混凝土抗碳化能力从高到低依次为:三掺粉煤灰+矿渣+硅灰,双掺粉煤灰+矿渣,双掺粉煤灰+硅灰,单掺矿渣,单掺粉煤灰,单掺硅灰.合理双掺粉煤灰+矿渣或三掺粉煤灰+矿渣+硅灰,不仅能使混凝土获得满足要求的抗碳化能力,还可以大大提高水泥取代量.     

Utilization of fly ash and ground granulated blast furnace slag as an alternative silica source in reactive powder concrete

Reactive powder concrete (RPC) is an ultra high strength cement-based material. Cement and silica fume (SF) content of RPC are generally rather high compared to the conventional concrete. The aim of this study is to decrease the cement and SF content of RPC using with fly ash (FA) and/or ground granulated blast furnace slag (GGBFS). The effect of these mineral admixtures on compressive strength of RPC has been investigated under autoclave curing. In the first stage, the effect of autoclave time and SF content on compressive strength was determined. In the second stage, SF was gradually decreased and cement was replaced with FA and/or GGBFS at different proportions. The microstructure was investigated by scanning electron microscope (SEM). Test results indicate that, the utilization of FA and/or GGBFS in RPC is possible without significant mechanical performance loss. SEM micrographs revealed the tobermorite having different morphology.     

Rheology of ordinary and low-impact environmental concretes

This study deals with the rheological properties of concrete mixtures incorporating various types of mineral additions as a partial replacement of cement in order to produce a low-impact environmental concrete. The control mixture contained only Portland cement as the binder, while the remaining mixtures incorporated binary cementitious blends of slag, limestone filler, and fly ash with different rates of replacement. After mixing, the plastic viscosity and yield stress of the concretes were evaluated at different slump values using a rheometer apparatus. The results showed that the type of mineral additions and the rate of substitution affect the rheological parameters of low-impact environmental concrete. Indeed, increasing the degree of substitution leads to an increase in the plastic viscosity of the concrete made with different types of additions used in this study.     

Research on optimizing components of microfine high-performance composite cementitious materials

The relationship between material components and mechanical properties was studied in terms of composite material principles and orthogonal experimental design. Moreover, the microstructure of microfine high-performance composite cementitious material (MHPCC) paste was investigated by means of scanning electron microscopy (SEM) methods. The results showed that the composite material consisting of blast furnace slag (BFS), gypsum (G₂) and expansive agent (EA) could obviously improve the strength of the cementitious material containing 40% fly ash (FA). Although microfine cement (MC) was merely 45% percent of the MHPCC, the compressive strength of MHPCC paste was higher than that of neat MC paste. BFS played an important role in MHPCC. The optimum-added quantity of BFS was 15%. The needle-shaped ettringite obtained from the EA reacting with Ca(OH)₂ forms a three-dimensional network structure, which not only improved the early strength of MHPCC paste but also increased its late strength. The reason was that the network structure, which was similar to a fiber-reinforced composite, was formed in the late period of hydration with the progress of hydration and the deposition of hydration products into the network structure.     

半柔性路面用水泥基灌浆材料的矿物掺合料协同优化研究

矿物掺合料是半柔性路面用水泥基灌浆材料的重要组成部分,各矿物掺合料协同优化对灌浆材料流动性能和力学性能的提升发挥重要作用。本文选用矿粉、微珠和硅灰三种矿物掺合料,通过正交试验研究了三种矿物掺合料协同优化对路面用灌浆材料流动性能和力学性能的影响规律,并借助XRD、SEM等表征方法分析了灌浆材料硬化浆体的水化产物组成与形貌。结果表明,三种矿物掺合料协同优化对灌浆材料流动性能和力学性能的影响顺序为微珠、硅灰和矿粉,其中微珠对灌浆材料流动性能改善效果最为显著,硅灰和矿粉对灌浆材料力学性能提升效果明显。以灌浆材料的流动性能和早期强度为评价指标,微珠、硅灰和矿粉协同优化灌浆材料的最佳掺量分别为15%、1.5%和5%(均为质量分数)。此外,三种矿物掺合料协同掺加对灌浆材料早期水化产物组成与形貌影响较小,表明矿物掺合料协同主要是通过物理填充作用提高了硬化浆体材料的密实度,从而改善灌浆材料早期力学性能。     

粉煤灰及其它矿物掺合料对新拌和硬化混凝土性能的影响

对超细粉煤灰、硅灰、稻壳灰、矿渣微粉四种矿物掺合料对混凝土用水量及混凝土强度的影响进行了比较研究 ,分析了矿物掺合料需水性的影响因素 ,并对各矿物掺合料的减水作用进行了排序。     

用Design-Expert软件研究掺合料对轻集料混凝土性能的影响

采用Design-Expert软件研究了矿物掺合料的种类及掺量对轻集料混凝土工作性能及力学性能的影响。结果表明:矿物掺合料掺入能够改善轻集料混凝土拌合物的工作性能,提高混凝土拌合物的匀质性;但粉煤灰掺入会降低轻集料混凝土的抗压强度,而硅灰掺入则能够提高轻集料混凝土的强度;本试验中各种矿物掺合料的最佳掺量为粉煤灰20%、矿粉10%、硅灰5%;使用Design-Expert软件能够准确有效分析矿物掺合料种类及掺量对轻集料混凝土性能的影响。     

Investigation on key properties controlling early-age stress development of blended cement concrete

Age dependent mechanical and kinetic properties including Young's modulus, early-age creep, autogeneous and thermal deformations, and heat of hydration were investigated for concrete made of blended cements. These are among the key properties that control the early-age cracking behavior in hydrating concrete members. Among the main goals of the investigation were to provide the experimental data and to study the effect of adding mineral additives such as fly ash (FA), ground granulated blast furnace slag (GGBF), and silica fume (SF) on the aforementioned properties. The age-dependent behavior of Young's modulus, creep compliance, and autogeneous shrinkage as functions of heat of hydration were modeled. We emphasized on mathematical modeling the viscoelastic properties of concrete. The equations obtained can be used as inputs needed to calculate the early-age stress development in concrete members.     

Effect of ultrafine mineral powder on the charge passed of the concrete

The effect of different ultrafine mineral powders (UFMP) and water-binder ratio (W/B) on the charge passed of concrete under 28 days standard curing was investigated in accordance with ASTM C1202-97. The results show that the charge passed of concrete with UFMP is obviously lower than that of the concrete without UFMP, and the order of reducing the charge passed is silica fume (SF)>fly ash (FA)>natural zeolite (NZ)>ground blast furnace slag (GBFS). The charge passed of concrete decreased with W/B reduced and the dosage of the UFMP increased.     

矿物掺合料与水胶比对混凝土耐久性的影响研究

为研究矿物掺合料与水胶比对混凝土耐久性的影响,测试了不同混凝土的抗氯离子渗透性、抗冻性、耐磨性和抗硫酸盐侵蚀性能,采用灰色关联分析的方法,分析了矿物掺合料掺量、水胶比和混凝土耐久性之间的关联程度和关联极性。研究结果表明:粉煤灰和矿渣粉掺入会提高混凝土的抗氯离子渗透性,并存在最佳掺量,本文水胶比为0.38的混凝土,粉煤灰和矿渣粉掺量为15%时,混凝土的抗氯离子渗透性最高。矿物掺合料掺量与混凝土相对动弹性模量、耐磨度和抗硫酸盐侵蚀系数为正关联;水胶比增大会导致混凝土的抗氯离子渗透性降低,与混凝土相对动弹性模量、耐磨度和抗硫酸盐腐蚀系数为负关联。     

Steam-cured concrete incorporating mineral admixtures

This paper explores the potential benefits of steam-cured concrete, particularly on mixes incorporating mineral admixtures. Twenty mixes with various combinations of Portland cement, fly ash (FA), slag and silica fume (SF) were investigated. For each mix, specimens were either standard-cured in a water bath of 27 °C or steam-cured at 55 °C maximum temperature over 8 h. For the materials and test conditions reported in this study, it was found that steam-cured concretes were more porous as indicated by the much higher sorptivity values compared with standard-cured specimens. Mixes with SF have the best performance and hold promise in precast manufacturing due to their high early strength development and low sorptivity values.     

岩棉炉渣水硬活性及其水泥砂浆的耐久性分析

为循环利用岩棉生产过程中排出的炉渣废料,将其磨成3个细度的粉体,分别与岩棉纤维粉、粉煤灰和粒化高炉矿渣粉(简称矿粉)进行对比分析.结果表明:炉渣主要化学成分及含量接近粉煤灰.炉渣中玻璃体含量较高,同时存在少量结晶相,结晶度为5.28％.提高炉渣粉磨细度可显著增加活性.450 kg/m2比表面积的炉渣粉强度活性指数比粉煤灰高出约10％,低于同等细度的矿粉.掺入炉渣粉的水泥砂浆试件抗渗和抗冻性优于粉煤灰砂浆,而低于矿粉砂浆试件.孔结构测试分析表明,炉渣粉水泥砂浆孔隙率和多害孔含量介于矿粉水泥砂浆和粉煤灰水泥砂浆之间.粉磨制备的岩棉炉渣粉体具备作为矿物掺合料的可行性.     

Combined effects of mineral admixtures and curing conditions on the sorptivity coefficient of concrete

The effect of mineral admixture and curing condition on the sorptivity of concrete are investigated. In the present work, the maximum particle size and the grading of coarse aggregate, the cement content and water/cement ratio of the concrete are kept constant. Then, in the ordinary Portland cement (OPC) 42.5 concrete, a portion of the sand is replaced by a mineral admixture such as fly ash (FA), limestone filler, sandstone filler or silica fume (SF). This paper presents the results of both the sorptivity coefficient and the compressive strength of OPC 42.5 concretes with these mineral admixtures, and concretes with OPC 32.5, blended cement (BC) or trass cement (TC). The results obtained indicate that the sorptivity coefficient of concrete decreases as the compressive strength of concrete increases. It is also shown that the sorptivity coefficient of concrete is very sensitive to the curing condition. The effect of curing condition on the sorptivity coefficient of concrete seems to be higher in low-strength concretes.     

Blast furnace slag or fly ash filled rigid polyurethane composite foams: A comprehensive investigation

Ground granulated blast furnace slag (BFS) and fly ash (FA) are iron-making industry and power plant byproducts, respectively. Although their use in concrete is quite common, investigation of the effects of these inorganic compounds on polymer properties is quite new, and their use as fillers in polymer foam composites has not yet been really explored. Their properties, such as high electrical resistivity, make them a good asset for use in rigid polyurethane foams that are widely used for insulation. In this study, a comprehensive investigation of the effect of BFS and FA on morphology, electrical and thermal conductivity, and rheological and mechanical properties of water-blown rigid polyurethane foams was performed. The relationship between these properties was examined. A relative enhancement of the properties is observed for filled foams, especially up to the percolation threshold. The results highlight a noticeable effect of the electrical percolation threshold on the different properties of foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47433.     

氯离子在掺不同矿物质掺合料高性能混凝土中的扩散性能

采用改进型电迁移法测试了氯离子在掺不同矿物质掺合料高性能混凝土中的扩散性能．研究表明：在混凝土中分别内掺磨细矿渣、粉煤灰、硅灰、膨胀剂均可提高混凝土的抗渗透性能(Cl^-扩散系数降低),其中以单掺硅灰效果最优;在混凝土中复掺膨胀剂和磨细矿渣或膨胀剂和粉煤灰,对提高混凝土抗渗透性能的效果优于单掺二者之一,也优于单掺效果最好的硅灰混凝土．复掺膨胀剂和细掺料后混凝土内部结构进一步优化、微观结构致密、微缺陷减少,由此,开发了一种低成本配制超高抗渗性混凝土的新途径。