Electric arc furnace slag as natural aggregate replacement in concrete production

Recycled materials in the building industry represent an attractive alternative to the consumption of natural resources. The paper shows results obtained by adding electric arc furnace slag (EAFs) as partial replacement of natural aggregates in concrete production. EAFs determines a significant increase in the compressive strength of concrete while it does not seem to affect the bending strength and drying shrinkage of cement mixtures. The concrete durability was approached by a careful chemical analysis and microstructural investigation of EAFs. The tendency to deteriorate seems negligible due to a low presence of amorphous and expansive compounds leading to an increase in volume. Moreover, the metals released, compared with the national legislation requirements, meet environmental standards.     

Durability of concrete made with EAF slag as aggregate

Electric arc furnace (EAF) slag, a by-product of steelmaking recovered after the oxidizing process, is useful when employed as aggregate in hydraulic concrete and bituminous mixtures. Concrete made with EAF oxidizing slag as an aggregate shows good physical and mechanical properties and further study of its durability will ensure greater reliability in its usage. This paper details a systematic study of slag concrete behaviour under severe test conditions. The tests were designed to evaluate the internal expansivity of the slag, its chemical reactivity with some components of the cement and its resistance to environmental agents, ice and moisture. The results indicate that the durability of slag concrete is acceptable, though slightly lower than that of conventional concrete. When the mix proportions are adequate, both the mechanical strength and the durability of slag concrete are satisfactory, although in less care mixes durability is likely to be impaired.Finally, leaching tests were performed to determine the environmental impact of the concrete, which, in comparison to results obtained directly from the slag, confirmed an important cloistering effect of the cementitious matrix on contaminant elements.     

Optimum content of copper slag as a fine aggregate in high strength concrete

This study investigated the mechanical properties of high strength concrete incorporating copper slag as a fine aggregate and concluded that less than 40% copper slag as sand substitution can achieve a high strength concrete that comparable or better to the control mix, beyond which however its behaviors decreased significantly. The workability and strength characteristics were assessed through a series of tests on six different mixing proportions at 20% incremental copper slag by weight replacement of sand from 0% to 100%. The results indicated that the strength of the concrete with less than 40% copper slag replacement was higher than or equal to that of the control specimen and the workability even had a dramatic growth. The microscopic view demonstrated that there were limited differences between the control concrete and the concrete with less than 40% copper slag content. It also suggested that the determination of the copper slag replacement level should consider with the desired compressive strength of concrete.     

冶金渣矿物掺合料对混凝土抗渗性的影响

本文扼要概述了当前混凝土抗渗耐久性的研究现状,并着重阐述了利用矿渣粉、钢渣粉等冶金渣矿物掺和料,分别进行单掺和复掺来改善混凝土抗渗耐久性的试验研究情况。     

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。      

Behavior of self compacting concrete containing ladle furnace slag and steel fiber reinforcement

Self compacting concrete mixtures with the use of ladle furnace slag as filler and steel fibers as reinforcement were produced and tested in the laboratory. Different contents of ladle furnace slag filler, ranging from 60 to 120 kg/m³, and steel fibers, ranging from 0% to 0.7%, were used. The different mixtures were tested in the fresh state for fluidity, passing ability and resistance to segregation and in the hardened state for compressive strength, fracture toughness, freeze-thawing resistance and chloride penetration resistance. The test results showed that ladle furnace slag can be used as filler for self compacting concrete, as adequate consistency and workability was achieved, while compressive strength and durability were improved. Ladle furnace slag can also be combined with steel fibers, which considerably increase fracture toughness, in order to produce a high performance self compacting concrete using a low-cost industrial by-product such as ladle furnace slag.     

Mix design of concrete for prestressed concrete sleepers using blast furnace slag and steel fibers

The application of ground granulated blast furnace slag (GGBFS) and steel fibers in prestressed concrete railway sleepers was investigated in this study. The use of GGBFS was considered as an eco-friendly material aimed at reducing CO₂ emissions and energy consumption as well as to enhance the durability performance of railway sleepers. Steel fibers improves the durability and structural performance in terms of crack control and reduction of spalling and can replace shear reinforcement. The mix proportions of the concrete incorporating GGBFS (56% GGBFS) and GGBFS with steel fibers (56% GGBFS and 0.75% steel fibers) were determined through a series laboratory tests and a life cycle assessment. These mixes satisfied the requirements of the Korean Railway Standard and resulted in improved flexural capacity as well as less CO₂ emissions compared with current railway sleepers. Using these mixes, a total of ninety prestressed concrete sleepers were produced in a factory under the same manufacturing process as current railway sleepers, and their mechanical properties as well as durability performance were evaluated. The mix with partial replacement of Type III Portland cement by GGBFS showed an improved resistance to chloride ion penetration and freeze-thaw cycles compared with the concrete used for current railway sleepers. However, these mixes were more vulnerable to carbonation. The mix with GGBFS and steel fibers (mix BSF) showed a slightly better durability performance than the mix with GGBFS only (mix BS), including better carbonation and freeze-thaw resistances. The mix BSF showed decreased chloride ion penetration depth than mix BS but showed a slightly higher chloride ion diffusion coefficient.     

Early-age restrained shrinkage cracking of GFRP-RC bridge deck slabs: Effect of environmental conditions

Most of codes and guidelines for glass fiber reinforced polymers (GFRP) - Reinforced Concrete (RC) are based on modifying corresponding formulas, originally developed for steel bars, taking into account the differences in properties and behavior between FRP and steel. The main objective of this research is to investigate the effect of cyclic environments on early-age cracking of GFRP-RC bridge deck slabs experimentally. Two full-scale (measuring 2500-mm long × 765-mm wide × 180-mm thick) cast-in-place slabs reinforced with similar amounts of reinforcement ratio of 0.7% with GFRP and steel bars, respectively, were tested in adiabatic laboratory conditions as control specimens. In comparison, two other GFRP-RC deck slabs were tested under freezing–thawing and wetting–drying conditions. The test results are presented in terms of materials degradation, cracking pattern, crack width, and spacing, and strains in reinforcement and concrete. Test results indicate that the minimum reinforcement ratio (0.7%) recommended by the Canadian Highway Bridge Design Code 2006 (CHBDC 2006) for bridge deck slabs reinforced with GFRP bars satisfied the serviceability requirements after being subjected to the simulated cyclic exposures.     

Carbonation behaviour of recycled aggregate concrete

This paper reviews the effect of incorporating recycled aggregates, sourced from construction and demolition waste, on the carbonation behaviour of concrete. It identifies various influencing aspects related to the use of recycled aggregates, such as replacement level, size and origin, as well as the influence of curing conditions, use of chemical admixtures and additions, on carbonation over a long period of time. A statistical analysis on the effect of introducing increasing amounts of recycled aggregates on the carbonation depth and coefficient of accelerated carbonation is presented. This paper also presents the use of existing methodologies to estimate the required accelerated carbonation resistance of a reinforced recycled aggregate concrete exposed to natural carbonation conditions with the use of accelerated carbonation tests. Results show clear increasing carbonation depths with increasing replacement levels when recycled aggregate concrete mixes are made with a similar mix design to that of the control natural aggregate concrete. The relationship between the compressive strength and coefficients of accelerated carbonation is similar between the control concrete and the recycled aggregate concrete mixes.     

碳酸化钢渣和矿渣作硅酸盐水泥混合材水化性能研究

通过对钢渣碳酸化前后的硅酸盐相提取及水化放热性能和将碳酸化钢渣和矿渣作为混合材的硅酸盐水泥的胶砂强度和水化产物种类的测定,以及对它们微观形貌的观察,研究了碳酸化钢渣对胶凝体系水化性能的影响.结果表明,碳酸化使钢渣中硅酸盐相的含量由47.06％下降至14.38％;碳酸化促进了钢渣的早期水化,抑制其后期水化;在配比相同的条件下,碳酸化钢渣-矿渣-硅酸盐熟料体系试样的3、28d抗压强度较未碳酸化钢渣-矿渣-硅酸盐熟料体系试样的高;碳酸化生成的CaCO3促进了熟料的水化;碳酸化钢渣促进了胶凝体系中AFt的生成,且生成水合碳铝酸钙.     

Structural concrete with incorporation of coarse recycled concrete and ceramic aggregates: durability performance

The growing difficulty in obtaining natural coarse aggregates (NCA) for the production of concrete, associated to the environmental issues and social costs that the uncontrolled extraction of natural aggregates creates, led to a search for feasible alternatives. One of the possible paths is to reuse construction and demolition waste (CDW) as aggregates to incorporate into the production of new concrete. Therefore, a vast and detailed experimental campaign was implemented at Instituto Superior Técnico (IST), which aimed at determining the viability of incorporating coarse aggregates from concrete and ceramic brick wall debris, in the production of a new concrete, with properties acceptable for its use in new reinforced and pre-stressed structures. In the experimental campaign different compositions were studied by incorporating pre-determined percentages of recycled coarse concrete aggregates and recycled coarse ceramic plus mortar particles, and the main mechanical, deformability and durability properties were quantified, by comparison with a conventional reference concrete (RC). In this article, these results are presented in terms of the durability performance of concrete, namely water absorption, carbonation and chlorides penetration resistance.     

Mechanical, durability and microstructural characteristics of ultra-high-strength self-compacting concrete incorporating steel fibers

Few researches are carried out in the Gulf area to study the feasibility of producing UHSC using available local materials with the inclusion of steel fibers, and investigate its properties and durability. Local available materials and the inclusion of steel fibers with different volume fractions are investigated to produce UHSC. Different mechanical properties are evaluated (compressive strength and splitting tensile strength). Durability of the concrete in high sulfate and high temperature condition (i.e. resembling Gulf environment) is evaluated. Also, chloride permeability, bulk chloride diffusion and electrical resistivity are evaluated. Test results indicate that local material can produce UHS–FRC. The ductility of the concrete is greatly improved by the incorporation of steel fibers and increases as the fiber volume increases. Chloride permeability, bulk chloride diffusion and electrical resistivity are affected by the volume fraction of steel fibers. The inclusion of steel fibers did not have significant effect on the durability of the concrete in the sulfate environment. Microstructural investigations of UHS–FRC concrete were also performed. The microstructural investigations shed some light on the nature of interfacial bond of fibers and the cement paste and its effect on its mechanical and fracture properties.     

Properties and durability of concrete produced using CO2 as an accelerating admixture

Carbon dioxide was investigated for use as a beneficial admixture to concrete as it was truck mixed. The reaction between the CO₂ and the hydrating cement creates finely distributed calcium carbonate reaction products that thereby influence the subsequent hydration. Comparisons of the fresh, hardened and durability properties were made between a reference concrete batch, a batch that contained a conventional accelerating admixture, and three batches subjected to a carbon dioxide addition. The optimum dose of carbon dioxide was found to reduce the time to initial set by 40% and increase the one and three day compressive strengths by 14% and 10% respectively. In comparison to the CO₂ batch, the conventional accelerator provided greater reductions in set time but lower early strength. Concrete durability test results indicated that the carbon dioxide process did not compromise the expected durability performance of the treated concrete. Carbon dioxide is a viable admixture to improve concrete performance.     

Evaluation of rutting potential for asphalt concrete mixes containing copper slag

Copper slag (CS) is a by-product of the copper extraction process, which can be used as coarse and/or fine aggregate in hot mix asphalt (HMA) pavements. This study used CS as a replacement of the fine aggregate with a percentage of up to 40% by total aggregate weight. The objective of this study was to evaluate the effect of CS on the rutting potential of the asphalt concrete mix using two methods. One method is based on the Dynamic modulus |E*| testing result. Actual pavement temperature data from a test section were used with the developed |E*| master curves. EverStressFE finite element program was used to perform a linear elastic load-deformation analysis for a pavement section and to determine the vertical resilient strain in a 40-mm HMA surface layer. The M-E PDG permanent deformation model was used with and Excel Visual Basic for Applications code to predict the accumulated rutting for different CS mixes for 10 million ESALs. The other method used the data from the flow number (FN) test. Based on the |E*| approach, the results indicated that adding 5% CS in the mix increased the predicted rutting from 0.59 to 0.98 mm at 10 million ESALs (increase by 68%). When 40% CS was used, rutting increased by more than 700% compared with the control mix. After analysing the FN results with the Francken model, the results indicated a decrease in FN as CS content is increased, indicating higher rutting potential. The decrease in FN ranged from 9% for 5% CS to 95% for 40% CS. The mixes containing up to 10% CS satisfied the minimum FN criteria for rutting. A calibration process for the M-E PDG distress prediction models that allows the use of waste and by-product materials such as CS should be considered in the future.     

Mechanical properties of concrete containing phase-change material

This study aimed to investigate the mechanical properties of concrete containing solid–liquid phase-change material (PCM) and focused on two key factors. First, a systematic study on the mechanical performance of PCM-modified concretes was conducted, including compressive, elastic modulus, and shrinkage tests. Second, because PCM provides high latent heat during the solid–liquid phase change, the effects of the solid phase and liquid phase on the mechanical properties of concrete were also explored. Results of this study showed that the solid–liquid phase of PCM affected the mechanical properties of concrete. For example, the compressive strength of 10% PCM concrete in solid phase (23 °C) and liquid phase (40 °C) at 28 days was 29.30 and 19.57 MPa, respectively. In addition, with increasing PCM content, the mechanical properties were degraded. For example, 10, 20, and 30% of PCM content lowered the compressive strength by 35.4, 58.4, and 74.3%, respectively. Therefore, concrete with PCM may not be suitable for structural elements. However, PCM is an important solution for optimizing energy consumption in modern buildings. It can absorb or emit large amounts of heat to store or release thermal energy. These properties can be used to control building temperatures resulting in energy saving and carbon reduction.     

Engineering properties of concrete containing natural zeolite as supplementary cementitious material: Strength,toughness, durability,and hygrothermal performance

A complex analysis of engineering properties of concrete containing natural zeolite as supplementary cementitious material in the blended Portland-cement based binder in an amount of up to 60% by mass is presented. The studied parameters include basic physical characteristics, mechanical and fracture–mechanics properties, durability characteristics, and hygric and thermal properties. Experimental results show that 20% zeolite content in the blended binder is the most suitable option. For this cement replacement level the compressive strength, bending strength, effective fracture toughness, effective toughness, and specific fracture energy are only slightly worse than for the reference Portland-cement concrete. The frost resistance, de-icing salt resistance, and chemical resistance to MgCl₂, NH₄Cl, Na₂SO₄, and HCl are improved. The hygrothermal performance of hardened mixes containing 20% natural zeolite, as assessed using the measured values of water absorption coefficient, water vapor diffusion coefficient, water vapor sorption isotherms, thermal conductivity, and specific heat capacity, is satisfactory.     

Properties of interfacial transition zones (ITZs) in concrete containing recycled mixed aggregate

Concretes containing mixed recycled aggregate (RA) have a larger number of coarse aggregate/paste interfacial transition zones (ITZs) than conventional concretes, due to the various component materials present in recycled aggregate. This study investigated the properties of various RA/paste ITZs in concrete using nanoindentation and scanning electron microscopy (SEM) and analysed the possible impact of the properties of the ITZs on the macro-mechanical performance of recycled concrete. It was found that the elastic modulus of the ITZ varies with the type of constituent materials present in recycled aggregate, with ITZs associated with organic components (e.g. wood, plastic and asphalt) exhibiting lower minimum elastic modulus values. The impact of ITZ properties on macro-mechanical properties of concrete depends on the relative content of different constituent materials present in the recycled aggregate and the micro-mechanical properties of the ITZs involved.     

Mechanical and durability properties of ternary concretes containing silica fume and low reactivity blast furnace slag

In this study, the effect of incorporation of silica fume in enhancing strength development rate and durability characteristics of binary concretes containing a low reactivity slag has been investigated. Binary concretes studied included mixes containing slag at cement replacement levels of 15%, 30% and 50% and mixes containing silica fume at cement replacement levels of 2.5%, 5%, 7.5% and 10%. Ternary concretes included combinations of silica fume and slag at various cement replacement levels. The w/b ratio and total cementitious materials content were kept constant for all mixes at 0.38 and 420 kg/m³ respectively. Concrete mixes were evaluated for compressive strength, electrical resistance, chloride permeability (ASTM C1202 RCPT test) and chloride migration (AASHTO TP64 RCMT test), at various ages up to 180 days.The results show that simultaneous use of silica fume has only a moderate effect in improving the slow rate of strength gain of binary mixes containing low reactivity slag. However it improves their durability considerably. Using appropriate combination of low reactivity slag and silica fume, it is possible to obtain ternary mixes with 28 day strength comparable to the control mix and improve durability particularly in the long term. Ternary mixes also have the added advantage of reduced water demand.     

Mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements

The benefits of limestone filler (LF) and natural pozzolana (NP) as partial replacement of Portland cement are well established. Economic and environmental advantages by reducing CO₂ emission are well known. However, both supplementary materials have certain shortfalls. LF addition to Portland cement causes an increase of hydration at early ages inducing a high early strength, but it can reduce the later strength due to the dilution effect. On the other hand, NP contributes to hydration after 28 days improving the strength at medium and later ages. Hence, ternary blended cement (OPC–LF–NP) with better performance could be produced. In this paper, mortar prisms in which Portland cement was replaced by up to 20%LF and 30%NP were tested in flexure and compressive strength at 2, 7, 28 and 90 days. Some samples were tested under sulfate and acid solutions and for chloride ions permeability. Results show that the use of ternary blended cement improves the early age and the long-term compressive and flexural strengths. Durability was also enhanced as better sulfate, acid and chloride ions penetration resistances were proved.