Improvement of the early-age reactivity of fly ash and blast furnace slag cementitious systems using limestone filler

This article analyzes the effects of the addition of limestone filler on the hydration rate, setting times and early-age mechanical properties of binary and ternary-binder mortars containing Portland cement, blast furnace slag (BFS) and fly ash (FA), with various substitution rates of cement with mineral additions going up to 50%. Vicat needle penetration tests and measurements of heat flow of reaction, compressive strength and dynamic Young’s modulus were carried out on 14 mortars prepared with binary and ternary binders, at 20°C. The results obtained on the mortars containing binary binders, show that their loss of mechanical strength at early age is not caused by a deceleration of the reactions of cement in the presence of mineral additions, but is mainly explained by the dilution effect related to the reduction in cement content. A moderate addition of limestone filler (8–17%) makes it possible to obtain ternary binders with early-age reactivity equal or even higher than that of Portland cement, and with 28-days mechanical resistance close to those of the binary-binder mortars. This accelerating effect of limestone filler is particularly sensitive in the case of mortars containing FA.     

Mechanical and cementitious characteristics of ground granulated blast furnace slag and basic oxygen furnace slag blended mortar

Reusing waste materials and reducing carbon emissions are crucial environmental concerns. Ground granulated basic oxygen furnace slag (GGBOS) and ground granulated blast furnace slag (GGBS) are the by-products of the steel industry and has positive effects on the environment because it reduces the problems associated waste disposal. This study reused these two products to completely replace cementitious materials, thus contributing to waste recycling, reducing the production demand for cement, and mitigating carbon emissions. Twelve mixture proportions were designed in this study, including an ordinary Portland mortar (OPM) as the control group and 11 steel/iron slag blended mortar (SISBM) experimental groups for the mechanical and cementitious characteristic experiments. The optimal mixing ratio for SISBM compressive strength ranged from GGBOS (steel slag): GGBS (iron slag) = 3:7 to 5:5 (by weight). At the age of 91 days, the compressive strength of SISBM reached 80–90% compared with that of the control group. Based on the pH values, free-CaO, and microanalysis results, the cementitious characteristics were mainly generated because the GGBOS increased the free-CaO or Ca(OH)₂ concentrations in the SISBM curing water and provided alkaline environments for Ca(OH)₂ to engage in the pozzolanic reaction with the SiO₂ and Al₂O₃ in GGBS, forming crystals such as calcium aluminum silicate hydrate, (C–A–S–H), calcium silicate hydrate (C–S–H), and calcium–magnesium–alumina–silicate (C–M–A–S), which generated strength and strengthened microstructure.     

Self-cleaning engineered cementitious composites

Engineered cementitious composite (ECC) is a strain hardening cementitious composite with extreme tensile ductility of several percent. Few emerging applications of ECC, including lightweight building façade and pavement, make self-cleaning a desirable functionality to be added into the material. This study aims to impart photocatalytic properties into ECC for engaging self-cleaning. Influence of TiO₂ content on mechanical properties, cleaning efficiency, surface wettability, and dirt pick-up resistance of white ECC was studied. It shows that the inclusion of TiO₂ in ECC engages photocatalysis, facilitates the decomposition of RhB, and enhances photo-induced hydrophilicity significantly. As a result, TiO₂-ECC possesses self-cleaning with higher dirt pick-up resistance than normal ECC. However, TiO₂ photocatalysis may adversely affect the flexural strength and ductility of ECC due to weakened fiber/matrix interface bond after UV/sunlight irradiation.     

Alkali activated slag pastes with surface-modified blast furnace slag

A surface modification method for blast furnace slag particles is newly proposed to retard the setting time and to mitigate the flow loss in alkali activated slag pastes. BFS particles were treated by a NaOH solution and then were carbonated to modify the surface of the particles. This leads to suppression of the dissolution of the reactive components at the initial stage of the reaction. The effect of the carbonation period and the modifying solution on the physicochemical characteristics of surface-modified BFS particles was investigated. The reaction and mechanical characteristics of AAS pastes produced from surface-modified BFS were also investigated. The test results show that the developed AAS pastes exhibited the delayed setting behavior and the retarded flow loss, and had a compressive strength comparable to those of AAS pastes produced from unmodified BFS.     

Water permeability of engineered cementitious composites

The water permeability of a unique class of high performance fiber reinforced cementitious composites (HPFRCC) called engineered cementitious composites (ECC) is investigated. These composites are deliberately tailored using microcmechanical design principles to exhibit pseudo-strain-hardening characteristics in uniaxial tension, up to greater than 4% strain. While undergoing tensile deformation, microcracks are designed to saturate the specimen rather than localize into large cracks. This tendency to form microcracks, which are experimentally shown to be approximately 60 μm in width, allows ECC material in the cracked state to maintain water permeability similar to that of uncracked concrete or mortar, and magnitudes lower than cracked reinforced mortar or concrete. It is also shown that the self-healing properties of cracks within ECC material significantly aids in reducing the coefficient of permeability of cracked ECC.     

Development of blast furnace slag mixtures against frost salt attack

Carbonation is considered to be one of the most detrimental processes contributing to the frost salt attack deterioration of blast furnace slag (bfs) concrete. In this paper, the application of sodium monofluorophosphate (Na-MFP) as a curing solution or surface pre-treatment compound to improve frost salt scaling resistance of carbonated bfs mortar was studied. It was found that the treated specimens were more durable against frost salt attack than a conventional mortar with air-entrainment. The optimum mixture design can be achieved by using a suitable dosage of air-entraining agent, along with the Na-MFP application. The experimental results show that the optimized mixtures have an acceptable frost salt scaling durability that is comparable to the performance of ordinary Portland cement mixtures. The results obtained from a natural exposure confirm this healing phenomenon.     

聚乙烯醇纤维增强钢渣粉-水泥复合材料基本力学性能及微观结构

通过掺加钢渣粉来制备聚乙烯醇（PVA）纤维增强钢渣粉-水泥基复合材料,从宏微观两个方面研究了这种复合材料的性能。考虑了基体材料的水胶比（0.25和0.35）、不同钢渣粉质量分数（0、30wt%、60wt%、80wt%）,采用抗压强度试验、薄板四点弯曲试验研究了PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能变化规律及其在弯曲荷载作用下的裂缝控制能力,采用扫描电镜观测了破坏后试样的微观结构。结果表明,水胶比和钢渣粉掺量均可明显影响PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能,在低水胶比条件下（水胶比为0.25）,钢渣粉掺量达到80wt%时,试样表现出较高的韧性指数和良好的裂缝控制能力,基本满足工程所需强度要求,水胶比为0.35时钢渣掺量不宜超过60wt%;同时,从节能减排的角度考虑,利用钢渣粉制备PVA纤维增强钢渣粉-水泥基复合材料是可行的。      

Effects of deicers on the performance of concrete pavements containing air-cooled blast furnace slag and supplementary cementitious materials

This study investigates the effects of continuous deicer exposure on the performance of pavement concretes. For this purpose, the differences in the compressive strength, the changes in the dynamic modulus of elasticity (DME) and the depth of chloride ingress were evaluated during and after the exposure period. Eight different concrete mixtures containing two types of coarse aggregates (i.e. air-cooled blast furnace slag (ACBFS) and natural dolomite) and four types of binder systems (i.e. plain Type I ordinary portland cement (OPC) and three combinations of OPC with fly ash (FA) and/or slag cement (SC)) were examined. These mixtures were exposed to three types of deicers (i.e. MgCl₂, CaCl₂, and NaCl) combined with two different exposure conditions (i.e. freezing-thawing (FT) and wetting-drying (WD)). In cold climates, these exposure conditions are the primary durability challenges that promote the physical deterioration of concrete pavements. The results indicated that among the studied deicers, CaCl₂ had the most destructive effect on the tested concretes while NaCl was found to promote the deepest level of chloride ingress yet was shown to have the least damaging impact on concretes. The microstructure evaluation revealed that the mechanism of concrete deterioration due to the deicer exposure involved chemical reactions between the deicers and concrete hydration products. The use of FA or SC as partial replacements for OPC can offset the detrimental effects of both deicers and FT/WD cycles.     

Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag

The mechanical properties (flexural strength, compressive strength, toughness and fracture energy) of steel microfiber reinforced reactive powder concrete (RPC) were investigated under different curing conditions (standard, autoclave and steam curing). Portland cement was replaced with ground granulated blast furnace slag (GGBFS) at 20%, 40% and 60%. Sintered bauxite, granite and quartz were used as aggregates in different series. The compressive strength of high volume GGBFS RPC was over 250 MPa after autoclaving. When an external pressure was applied during setting and hardening stages, compressive strength reached up to 400 MPa. The amount of silica fume can be decreased with increasing amount of GGBFS. SEM micrographs revealed the tobermorite after autoclave curing.     

On the shear behavior of engineered cementitious composites

Results of an experimental investigation of structural response of shear beams made of a special class of cementitious composites, referred to as engineered cementitious composites (ECCs), are reported. ECCs are designed with tailored material structure and have been shown to exhibit pseudo strain-hardening tensile behavior. The improved performance in shear over conventional plain, fiber-reinforced, and wire mesh reinforced concrete is demonstrated. It is suggested that ECCs can be utilized for structural applications where superior ductility and durability performance are desired.     

超高韧性水泥基复合材料自愈合研究进展

在总结了最近几年国内外相关研究进展的基础上,对超高韧性水泥基复合材料(ECC)及裂缝自愈合进行了综述。着重介绍了裂缝自愈合的最大允许宽度限值以及自愈合机制。提出利用ECC所独具的对裂缝宽度的可控性及紧密细小的微裂纹、较低的水胶比及矿物掺合料的二次水化效应可实现其良好的自愈合特性。最后指出该研究领域所面临的挑战及今后的研究方向,为ECC裂缝自愈合的研究提供有价值的理论参考。     

Design of self-compacting concrete with ground granulated blast furnace slag

Ground granulated blast furnace slag (GGBS), due to its pozzolanic nature, could be a great asset for the modern construction needs, because slag concretes can be of high performance, if appropriately designed. The use of GGBS as a cementitious material as well as fine filler is being increasingly advocated for the production of High Performance Concrete (HPC), Roller Compacted Concrete (RCC) and self compacting concrete (SCC), etc. However, for obtaining the required high performance in any of these concrete composites, slag should be properly proportioned so that the resulting concrete would satisfy both the strength and performance criteria requirements of the structure. The present paper is an effort towards presenting a new mix design methodology for the design of self compacting GGBS concretes based on the efficiency concept. The methodology has already been successfully verified through a proper experimental investigation and the self compacting slag concretes were evaluated for their self compactability and strength characteristics. The results indicate that the proposed method can be capable of producing high quality SCC.     

Removal of phosphate from aqueous solution with blast furnace slag

Blast furnace slag was used to remove phosphate from aqueous solutions. The influence of pH, temperature, agitation rate, and blast furnace slag dosage on phosphate removal was investigated by conducting a series of batch adsorption experiments. In addition, the yield and mechanisms of phosphate removal were explained on the basis of the results of X-ray spectroscopy, measurements of zeta potential of particles, specific surface area, and images of scanning electron microscopy (SEM) of the particles before and after adsorption. The specific surface area of the blast furnace slag was 0.4m(2)g(-1). The removal of phosphate predominantly has taken place by a precipitation mechanism and weak physical interactions between the surface of adsorbent and the metallic salts of phosphate. In this study, phosphate removal in excess of 99% was obtained, and it was concluded that blast furnace slag is an efficient adsorbent for the removal of phosphate from solution.     

Hydration of alkali-activated ground granulated blast furnace slag

The hydration of ground granulated blast furnace slag (GGBFS) at 25 °C in controlled pH environments was investigated during 28 days of hydration. GGBFS was activated by NaOH, and it was found that the rate of reaction depends on the pH of the starting solution. The main product was identified as C-S-H, and, in the pastes with high pH, hydrotalcite was observed at later stages of hydration. The pH of the mixing solution should be higher than pH 11.5 to effectively activate the hydration of GGBFS. As deduced from very low electrical conductivity measurements, GGBFS pastes had very tortuous and disconnected pores. The effect of the pH of the aqueous solution on the composition, microstructure and properties of alkali-activated GGBFS pastes are also discussed.     

Effect of granulometry on cementitious properties of ladle furnace slag

Ladle furnace slag (LFS), a by-product of the steel making process, was tested for its potential use as a supplementary cementing material. The material used for the tests was screened or ground, producing three samples of different fineness, and the granulometry of these LFS samples was also tested by particle size analysis. Their chemical and mineralogical composition was assessed by chemical analysis, X-ray diffraction and thermogravimetric analysis. Finally, in order to determine the cementitious and pozzolanic character of LFS in relation to its granulometry, slag-lime and slag-cement mortars were produced and tested in compression. The results show that although LFS is a weak supplementary cementing material, it shows some self-cementing and pozzolanic properties that can be enhanced by screening or grinding the raw material. Even though different levels of fineness and granulometry can be reached with each method, generally, grinding seems to improve LFS binding properties more than sieving.     

Behavior of unreinforced masonry prisms and beams retrofitted with engineered cementitious composites

The impact of a thin layer of a ductile fiber-reinforced concrete referred to as engineered cementitious composites (ECC) on unreinforced masonry (URM) prisms and beams has been evaluated. The objective of the research was to characterize the performance and potential benefits of using ECC to retrofit URM with eventual application to masonry infill walls in non-ductile reinforced concrete frames. Compression tests of masonry prisms and flexural tests of masonry beams with different ECC retrofit schemes were conducted. The variables studied were the use of wall anchors to improve the ECC-masonry bond and alternate steel reinforcement ratios within the ECC layer in the form of welded wire fabric. The ECC retrofit was found to increase the strength and stiffness of URM prisms by 45 and 53 %, respectively compared to those of a plain specimen. When wall anchors were installed on the masonry specimens, the bond between the ECC layer and the masonry surface was improved. Four-point bending tests indicated that the strength and more importantly the ductility of an ECC retrofitted brick beam are increased significantly, especially when light reinforcement is added to the ECC layer, relative to an URM beam. Analytical models for estimating the strength and stiffness of ECC retrofitted masonry specimens are proposed and evaluated.     

改性高炉渣作为矿渣棉原料的实验研究

研究了加入不同比例铁矿废石或粉煤灰的高炉矿渣成分的变化,及对矿渣作为制备矿渣棉原料的影响,并对其影响机制进行了分析.结果表明,随着铁矿废石或粉煤灰配加比例的增加,矿渣中SiO2和Al2O3总含量逐渐升高,CaO、MgO、Fe2O3、FeO、K2O和Na2O的总含量降低,矿渣酸度系数Mk和粘度系数Mη值升高,氢离子指数pH值降低,熔渣粘度增加,但是在高温区粘度变化较小;由此可以预测,上述成分的改性矿渣更适合制备矿渣棉纤维.     

Mechano-chemical modification of cement with high volumes of blast furnace slag

The application of chemical admixtures significantly improves the performance of cement-based materials. Some admixtures can also be used to modify the cement grinding process and induce changes in the structure of cement minerals due to mechano-chemical activation. A reactive silica-based complex admixture was developed for the modification of cement grinding. This paper examines the effect of grinding on the strength of a modified cement containing granulated blast furnace slag in high volumes. According to the test results, mortars based on the modified cement possess a compressive strength of up to 91.7 MPa, a 62% increase over the reference.