Çimento esaslı kompozitlerin çelik lif-matris aderansı özellikleri

Çelik lifli betonların mekanik özelliklerini etkileyen en önemli faktörlerden biri lif-matris aderansıdır. Lifli betonlar kompozit malzeme oldukları dolayısıyla çekme kuvetlerini lif ve matris ile kompozit bir davranışla karışılamaktadırlar. Bu sebepten dolayı aderans özellikleri lif ve matris arasında yük transferini etkiliyebilmektedir. Bu çalışmanın esas amacı çekip-çıkarma deneyi yöntemi ile lif-matris aderansını etkileyen bazı faktörlerin araştırılmasıdır. Matris olarak geneleksel çimento esaslı bir harç (OM) ve reaktif pudra beton (RPC) kullanılmıştır. Lifin kancalı ve kancasız durumu, lif gömme boyu, su/bağlayıcı oranı, hamur fazın etkisi, ve kür koşulları gibi parametrelerin lif-matris aderansında etkileri araştırılmıştır. Ayrıca karışımların mekanik özellikleri belirlenmiştir. İkinci aşamada bazı kimyasal katkıların OM ve RPC karışımların lif-matris aderansı özelliklerinde etkisi araştırılmıştır. Dört farklı polimer, bir korozyon inhibitörü ve bir su geçirimsizlik sağlayan katkı kullanılmıştır. Ayrıca karışımların taze hal, mekanik ve fiziksel gibi özellikleri?de belirlenmiştir. Lif-matris arayüzey özelliklerini daha detaylı irdelemek için iç yapı çalışmaları yapılmışrır. Ayrıca metalürji mühendisliği ve korozyon mühendisliğinin çalışmalarında kullanılan elektrokimyasal yöntemlerden polarizasyon tekniği ile çelik lif korozyon gelişimini izlenmiştir. The fiber-matrix bond characteristic is one of the most important factors which affect the mechanical properties of various steel fiber reinforced concretes (SFRC). Forasmuch as SFRC resists tensile forces as a composite material by its fiber and matrix phases, the fiber-matrix bond affects force transmission between them. The aim of this research is to investigate some of the factors which affect the steel fiber-matrix bond characteristics by means of pull-out test. Ordinary mortar (OM) and reactive powder concrete (RPC) was used as main matrices. The effect of parameters such as end condition of fiber (smooth or hooked-end), embedment length, water/binder ratio, paste phase of RPC, steel-micro fiber, and curing conditions on fiber-matrix pull-out behavior were determined. The mechanical properties of the mixture were also analyzed. In the second stage, the effect of some chemical admixtures on fiber-matrix bond characteristic of OM and RPC mixtures were investigated. Four polymer based, a corrosion inhibitor, and a waterproofing admixture were used in this stage of study. Additionally, fresh states, mechanical properties, chloride ion patentability, and physical properties of the mixtures were determined. Microstructural analysis was also performed to evaluate the microstructure of fiber-matrix interface of mixtures. Corrosion of steel fiber was also monitored by polarization technique which is widely utilized in the metallurgy and corrosion engineering

Pull-out behavior of steel fiber embedded in flowable RPC and ordinary mortar

The aim of this research is to investigate some of the factors which affect the steel fiber-matrix bond characteristics by means of pull-out test. Ordinary mortar (OM) and reactive powder concrete (RPC) were used as main matrices. The effect of parameters such as end condition of fiber (smooth or hooked-end), embedment length, water/binder ratio, paste phase of RPC, steel-micro fiber, and curing conditions on fiber-matrix pull-out behavior were determined. The fiber-matrix bond characteristics improved as the embedment length of fiber increased, especially for smooth fiber. Low W/C ratio, which enhances the bond strength, reduces the importance of embedment length of the hooked-end fiber. Furthermore, the pull-out peak load and debonding toughness increased as the W/C ratio decreased in the all curing conditions. Microstructural investigation revealed that the congestion of hydration products in fiber-matrix interface improves pull-out behavior remarkably. (C) 2014 Elsevier Ltd. All rights reserved

The effect of alkali-silica reaction on steel fiber-matrix bond characteristics of cement based mortars

The effect of ASR on fiber-matrix bond behavior has been investigated in this research. The potentially reactive basaltic aggregate was chosen as a reactive material. Two series of specimens containing different amounts of supplementary cementing materials (SCMs) were prepared. One of them was cured in 1 M NaOH solution at 80 degrees C, other series were cured in 80 degrees C water up to 150 days to obtain similar maturity. ASR expansion, single fiber pull-out load, debonding toughness, flexural and compressive strength was determined. Test results indicate that the ASR gel congestion in fiber-matrix interface increased the bond strength significantly during alkali exposure. Furthermore, SCMs are effective to reduce ASR expansion and to prevent the mechanical properties loss due to ASR. Micro-structural investigations revealed the reaction products having different morphology (fibrous, rosette type, network appearance, etc.) in alkali exposed specimens. (C) 2013 Elsevier Ltd. All rights reserved

Autoclaved reactive powder concrete: the effects of steel micro-fibers and silica fume dosage on the mechanical properties

Reactive Powder Concrete (RPC) is a type of ultra-high performance cement based composite with high strength and ductility. RPC was developed in the 1990s by Bouygues' laboratory in France. It is a special type of concrete which has properly optimized micro grain, binder phase and steel micro-fibers. RPC can achieve compressive strength values between 150–800 MPa, while traditional concrete which is used in current structures usually has 20–50 MPa compressive strength. In addition, its high performance under flexural loads is the most important advantage of RPC in the field of civil engineering. RPC has the potential to compete with steel from the point of aesthetics and structural capability. One of the curing methods to enhance the strength of this composite material is autoclaving. Autoclave curing needs additional SiO2 source to fill micro pores and strengthen hydration products. In the scope of this study, the effect of volume fraction of steel micro-fibers and silica fume dosage as SiO2 source on mechanical properties of RPC under autoclave curing was investigated. High performance cementitious composites were produced with 0%, 1%, and 2% volume fractions of steel micro-fibers. Nine mixtures with three different silica fume dosages were produced. Workability of fresh state and flexural-compressive strengths of hardened specimens were determined. In addition, fracture energies of the mixtures under bending loads were evaluated

Transport properties and freeze-thaw resistance of mortar mixtures containing recycled concrete and glass aggregates

The effects of recycled glass (RG) and recycled concrete (RC) fine aggregates on the compressive strength, ultrasonic pulse velocity, dynamic elastic modulus, transport properties and freeze-thaw resistance of mortar mixture were investigated comparatively. Nine different mortar mixtures were prepared by partial replacement of crushed-limestone fine aggregate with recycled aggregates. Compared to that of the control mixture, the transport properties of RC aggregate-bearing mixtures inversely affected with increasing the replacement level of this aggregate. The opposite results were obtained in RG aggregate-containing mixtures. Frost resistance of mortar mixture improved by using both of the recycled aggregates. Improvement of frost resistance of RC mixtures was attributed to the presence of improved Interfacial transition zone between matrix and coarse aggregate (ITZ) in RC-bearing mixture and to the high number of pores existing in the well-distributed RC aggregates in the mixture. Perhaps, these pores provide additional sites for the water escaped from capillary pores upon ice formation

Mitigation of Detrimental Effects of Alkali-Silica Reaction in Cement-Based Composites by Combination of Steel Microfibers and Ground-Granulated Blast-Furnace Slag

The effect of combining brass-coated steel microfiber and ground-granulated blast-furnace slag (GGBS) on the mitigation of deleterious expansion due to alkali-silica reaction (ASR) was investigated in this research. A potentially reactive basaltic aggregate was chosen as a reactive material. Two series of specimens containing different amounts of microfiber were prepared. One of them was cured in 1 M NaOH solution at 80 degrees C to obtain a similar maturity; the other series was cured in 80 degrees C water up to 120days. ASR expansion, strength development, and toughness properties were observed for 120 days in NaOH solution and the results were compared with specimens kept in water. Test results indicate that the combination of GGBS and steel fibers reduced ASR expansion significantly. Furthermore, the combination was very effective at preventing the mechanical property loss due to ASR, such as flexural strength, compressive strength, and toughness. Microstructural investigations revealed that the reaction products had a different morphology (e.g.,fibrous, network appearance) when the specimens were kept in NaOH solution

Electrochemical corrosion monitoring of steel fiber embedded in cement based composites

Steel fibers are commonly used in cement based materials for many applications such as floors, structural elements, repairing works, etc. The chloride-induced corrosion via ingress of seawater may become a risk for performance of the steel fiber reinforced cement based composites. Despite of few studies that have dealt with the corrosion behavior of steel fibers embedded in cement based composites, there are lack of information about the chloride-induced corrosion of steel fibers embedded with sufficient cover in non cracked matrixes, reactive powder concrete, and especially polymer-modified cement based mortars. The open-circuit potential and corrosion current density of single steel fibers embedded in various cement based matrices were monitored after 200, 400, 600, 1200 wetting-drying cycles in 3.5% NaC1 solution. The corrosion and microstructure analyses revealed that the steel fibers can be protected by a well designed mixture, non-cracked matrix and sufficient cover. However, it could be corroded in long terms depending on the type and the dosage of the polymer latex used. In addition, the residual stresses in the deformed regions of the hooked-end steel fibers is critical in terms of the protection against to chloride-induced corrosion. (C) 2017 Elsevier Ltd. All rights reserved