Effects of Redispersible Polymer Powder on Mechanical and Durability Properties of Preplaced Aggregate Concrete with Recycled Railway Ballast

The rapid-hardening method employing the injection of calcium sulfoaluminate (CSA) cement mortar into voids between preplaced ballast aggregates has recently emerged as a promising approach for the renovation of existing ballasted railway tracks to concrete tracks. This method typically involves the use of a redispersible polymer powder to enhance the durability of the resulting recycled aggregate concrete. However, the effects of the amount of polymer on the mechanical and durability properties of recycled ballast aggregate concrete were not clearly understood. In addition, the effects of the cleanness condition of ballast aggregates were never examined. This study aimed at investigating these two aspects through compression and flexure tests, shrinkage tests, freezing-thawing resistance tests, and optical microscopy. The results revealed that an increase in the amount of polymer generally decreased the compressive strength at the curing age of 28 days. However, the use of a higher polymer ratio enhanced the modulus of rupture, freezing-thawing resistance, and shrinkage resistance, likely because it improved the microstructure of the interfacial transition zones between recycled ballast aggregates and injected mortar. In addition, a higher cleanness level of ballast aggregates generally improved the mechanical and durability qualities of concrete

Value added utilization of by-product electric furnace ferronickel slag as construction materials: A review

This paper reviews the potential use of electric furnace ferronickel slag (FNS) as a fine aggregate and binder in Portland cement and geopolymer concretes. It has been reported that the use of FNS as a fine aggregate can improve the strength and durability properties of concrete. Use of some FNS aggregates containing reactive silica may potentially cause alkali-silica reaction (ASR) in Portland cement concrete. However, the inclusion of supplementary cementitious materials (SCM) such as fly ash and blast furnace slag as partial cement replacement can effectively mitigate the ASR expansion. When finely ground FNS is used with cement, it shows pozzolanic reaction, which is similar to that of other common SCMs such as fly ash. Furthermore, 20% FNS powder blended geopolymer showed greater strength and durability properties as compared to 100% fly ash based geopolymers. The utilization of raw FNS in pavement construction is reported as a useful alternative to natural aggregate. Therefore, the use of by-product FNS in the construction industry will be a valuable step to help conservation of natural resources and add sustainability to infrastructures development. This paper presents a comprehensive review of the available results on the effects of FNS in concrete as aggregate and binder, and provides some recommendations for future research in this field

Recycle of ground granulated blast furnace slag and fly ash on eco-friendly brick production

Use of industrial by-products as waste-based materials in the building industry has recently received significant attention to develop eco-friendly building materials. This paper presents an experimental study on properties of bricks containing clay, ground granulated blast furnace slag (GGBS) and fly ash (FA) at 850, 950 and 1050 °C. Physical, mechanical, thermal tests and microstructural analyses were performed. Results show that an increase in firing temperature results in a decrease in porosity and an increase in the bulk density and compressive strength of bricks. Results also show that an increase in the FA content results in an increase in porosity and water absorption but a decrease in bulk density, compressive strength, and thermal conductivity of the bricks. GGBS content has much less significant influence on porosity, water absorption, bulk density and thermal conductivity of bricks, but an increase in GGBS content leads to a significant increase in compressive strength of bricks. Even the binary brick with 30% GGBS/10% FA exhibits nearly identical properties to the control brick. These highly promising findings suggest that replacement of clay with industrial by-products can provide eco-friendly bricks, the use of which would contribute toward reducing the environmental impact of abundant waste products and conserving non-renewable natural resources. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group