Effect of nano and micro-silica on bond behaviour of steel and polypropylene fibres in high volume fly ash mortar

This paper presents the effects of nano silica (NS), micro silica (MS) and combined NS and MS on bond behaviour of steel and polypropylene (PP) fibres in high volume fly ash (HVFA) mortar. Three types of bend configuration of hook-end steel fibre commercially available are considered, while the PP fibre was crimped shape. Three different fly ash contents of 40%, 50% and 60% (by wt) as partial replacement of ordinary Portland cement (OPC) are considered in HVFA mortar, while a control mortar containing 100% OPC was also considered. The NS and the MS was added as 2% and 10% (by wt), respectively as partial replacement of OPC in HVFA mortar containing 40% fly ash. In the case of combined NS and MS, 2% NS and 10% MS was used as partial replacement of OPC in HVFA mortar. However, in the case of HVFA mortars containing 40% fly ash and different NS and MS, total OPC content of 60% was kept constant in all HVFA mixes containing NS, MS and NS + MS. This was considered to compare these mixes with HVFA mortar containing 40% fly ash. Results indicate that maximum pull-out force of both steel and PP fibres decreases with increase in fly ash contents in HVFA mortars at both 7 and 28 days.The addition of 2% NS and 10% MS showed almost similar improvement in the maximum pull-out force of steel and PP fibres at both ages in HVFA mortar containing 40% fly ash. The combined use of 2%NS + 10%MS also improved the maximum pull-out force and higher than 2% NS and 10% MS. The reduction in large capillary pores in HVFA mortars containing nano and micro silica observed in Mercury Intrusion Porosity test improved the bond of steel and PP fibres in those mortar due to formation of additional calcium silicate hydrate (C-S-H) gel is believed to be the reason behind this improvement. The maximum pull-out force also increased with increase in number of bends in the hook-end of steel fibre in all mortars in this study at both 7 and 28 days. Extra energy absorbed by the higher number of bends is the reason of such improvement in maximum pull-out force. However, in the case of absorbed energy mixed results are observed in the case of different number of bends in steel fibre ends. Good correlations also exist between the maximum pull-out forces of all three types of steel fibres with compressive strength of mortars showing strong influence on the bond behaviour

Pull-out Behaviour of Hooked End Steel Fibres Embedded in Ultra-high Performance Mortar with Various W/B Ratios

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bondslip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work

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

Lightweight building blocks incorporating bottom ash aggregate under different curing conditions

In this study, the utilization of bottom ash as an aggregate in the production of lightweight building blocks was investigated. Pumice aggregate which was used in lightweight control mixture replaced by the bottom ash aggregate and on the other hand, cement replaced by high volume fly ash. Physical and mechanical properties of mixtures were determined after different curing regimes (standard water, in air, in oven, steam and autoclave curing) and in addition, water resistance of the mixtures was also determined. After that, microstructure of the specimens was investigated by using the scanning electron microscopy. Then, the thermal conductivity of the mixtures containing pumice and bottom ash was compared. Finally, in order to produce construction elements, prototypes of lightweight building blocks were manufactured. After these very procedures, it concludes that bottom ash is a good alternative for pumice aggregate in producing lightweight building blocks

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