Showing papers on "Ground granulated blast-furnace slag published in 2016"

The pore solution of blended cements: a review

Abstract: This paper is the work of working group 3 of the RILEM Technical Committee on Hydration and Microstructure of Concrete with SCM (TC 238-SCM). The pore solution is an essential but often overlooked part of hydrated cements. The composition of the cement pore solution reflects the ongoing hydration processes and determines which solid phases are stable and may precipitate, and which phases are unstable and may dissolve. The study of the cement pore solution therefore contributes to the understanding of the mechanisms as well as of the kinetics of cement hydration. This paper reviews the impact of supplementary cementitious materials (SCMs) on the pore solution composition of blended cements. In a first part, the extraction and analysis methods of cement pore solutions are reviewed, leading to a set of practical guidelines and recommendations. In a second part, an extensive literature survey is used to document the effect of the addition of SCMs (blast furnace slag, fly ash and silica fume) on the pore solution. Finally, in a third part the collected literature data are compared to thermodynamic simulations. The performance and current limitations of thermodynamic modelling of blended cement hydration are demonstrated and discussed in view of future progress.

Sustainable use of industrial-waste as partial replacement of fine aggregate for preparation of concrete – A review

Abstract: Utilisation of industrial waste materials in concrete compensates the lack of natural resources, solving the disposal problem of waste and to find alternative technique to safeguard the nature. There are a number of industrial wastes used as fully or partial replacement of coarse aggregate or fine aggregate. This review carries out a thorough assessment about industrial waste substances, which can be adequately utilised in concrete as fine aggregate substitution. This paper reviewed some of these industrial wastes like waste foundry sand, steel slag, copper slag, imperial smelting furnace slag (ISF slag), blast furnace slag, coal bottom ash, ferrochrome slag, palm oil clinker etc. Out of these materials, maximum number of experiments have been conducted using waste foundry sand and copper slag as fine aggregate replacement, but still more examinations are required for other waste materials as replacement of sand in concrete. Different physical and mechanical properties of industrial waste as well as of industrial waste concrete, in which natural sand is substituted have been reviewed and comparisons are made between them. Deflection and leaching study review are carried out additionally and compared. It can be observed that the concrete where sand is replaced by copper slag, imperial smelting furnace slag, class F fly ash exhibits improved strength and durability properties, but it’s slump increases as the rate of replacement increases in the case of copper slag and the slump decreases in the case of class F fly ash. There is a less research work reported on ferrochrome slag and palm oil clinker used as sand substitution, so it is felt that further detailed investigations are required.

Ultra-high-ductile behavior of a polyethylene fiber-reinforced alkali-activated slag-based composite

Abstract: This paper presents an experimental study of the meso-level composite properties of an ultra-high-ductile polyethylene-fiber-reinforced alkali-activated slag-based composite. Four mixtures with 1.75 vol% of polyethylene fibers were prepared with varying water-to-binder ratio. The viscosity of the matrix was controlled to ensure a uniform fiber dispersion. A series of experiments, including density, compression, and uniaxial tension tests, was performed to characterize the mechanical properties of the composite. The test results showed that the average tensile strength to compressive strength ratio of the composites was 19.8%, nearly double that of normal concrete, and the average crack width was 101 μm. It was also demonstrated that tensile strain capacity and tensile strength of up to 7.50% and 13.06 MPa, respectively, can be attained when using the proposed polyethylene-fiber-reinforced alkali-activated slag-based composites.

Microstructural and Mechanical Properties of Alkali Activated Colombian Raw Materials.

Abstract: Microstructural and mechanical properties of alkali activated binders based on blends of Colombian granulated blast furnace slag (GBFS) and fly ash (FA) were investigated. The synthesis of alkali activated binders was conducted at 85 °C for 24 h with different slag/fly ash ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100). Mineralogical and microstructural characterization was carried out by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and Nuclear magnetic resonance (NMR). Mechanical properties were evaluated through the compressive strength, modulus of elasticity and Poisson's ratio. The results show that two different reaction products were detected in the slag/fly ash mixtures, a calcium silicate hydrate with Al in its structure (C-A-S-H gel) and a sodium aluminosilicate hydrate (N-A-S-H gel) with higher number of polymerized species and low content in Ca. It was found that with the increase of the amount of added slag, the amount of C-A-S-H gel increased and the amount of N-A-S-H gel decreased. The matrix was more dense and compact with almost absence of pores. The predominance of slag affected positively the compressive strength, Young's modulus and Poisson's ratio, with 80% slag and 20% fly ash concrete being the best mechanical performance blend.

The effect of high temperature on the design of blast furnace slag and coarse fly ash-based geopolymer mortar

Abstract: In this study, geopolymer mortars were prepared by replacing blast furnace slag (BFS) based mixtures with coarse fly ash (FA) in different proportions. The aim of this study was to build a geopolymer mortar design for high temperatures using constant NaOH molarity (M) and constant curing temperature. In addition to 14 M NaOH solution and BFS as the binder material at a 60 °C curing temperature, double binder mixture ratios were prepared adding 25%, 50% and 75% FA. Geopolymer mortars with a liquid binder (L/B) ratio of 1 were subjected to oven curing for 5, 24, 48, 168 h. After physical and mechanical tests, the samples with the highest compressive strength were determined and six different mixtures with an L/B ratio in the range from 1 to 0.5 were prepared in order to increase the compressive strength of the samples in question. The physical and mechanical tests were repeated for the new samples. After the tests, the mortar sample with the highest compressive strength and its high temperature behavior was determined. For this purpose, the mortar sample with the highest compressive strength was subjected to temperatures of 200, 400, 600, 800 and 1000 °C, and changes in the physical and mechanical properties was analyzed. As a result of the experiments, the highest flexural strength value (3.6 MPa) was obtained from the mortar samples with a 25% BFS content subjected to curing for 5 h. The highest compressive strength values (27.3 MPa) were obtained from the mortar samples with a 100% BFS content subjected to curing for 48 h. In terms of compressive strength, the optimization of the L/B ratio resulted in a 28% increase (0.7) and this way, 35.1 MPa was achieved. Following the high temperature tests, 400 °C and 600 °C were determined as critical temperatures for changes in mechanical properties and changes in physical properties, respectively. However, the geopolymer mortars lost around 58% of strength at 1000 °C which is the final temperature.

Stabilization of Demolition Materials for Pavement Base/Subbase Applications Using Fly Ash and Slag Geopolymers: Laboratory Investigation

Abstract: The use of recycled construction and demolition (C&D) materials in unbound and cement stabilized pavement base/subbase applications has generated growing interest in recent years. C&D materials consisting of crushed brick (CB), recycled crushed aggregate (RCA), and reclaimed asphalt pavement (RAP) have been investigated in unbound and cement stabilized pavement base/subbase applications. However, the high carbon footprint of using cement for pavement base/subbase stabilization has led to this research to seek alternative low-carbon binders. This study evaluates the behavior of C&D materials when stabilized with geopolymers. Fly ash (FA) and ground granulated blast furnace slag (S) were used as pozzolanic binders and a different alkaline activator solution to pozzolanic binder ratio was tested. A maximum of 4% of dry weight of soil was used for geopolymer stabilization of the C&D materials. The binders used were either 4% FA, 2% FA+ 2% S, or 4% S. The geotechnical engineering and strength propertie...

Creep and drying shrinkage of a blended slag and low calcium fly ash geopolymer Concrete

Abstract: The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2 % of low calcium fly ash and only 14.8 % of ground granulated blast furnace slag. Both drying shrinkage and creep are studied. In addition, different curing conditions at elevated temperature were used. All experimental results were compared to predictions made using the Eurocode 2. The curing regime plays an important role in the magnitude and development of both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of 3 days at 40 °C or 1 day at 80 °C is required to obtain final drying shrinkage strains similar to or less than those adopted by Eurocode 2 for ordinary Portland cement (OPC) concrete. Creep strains were similar or less than those predicted by Eurocode 2 for OPC concrete when the geopolymer concrete was cured for 3 days at 40 °C. After 7 days at 80 °C, creep strains became negligible.

Rapid screening tests for supplementary cementitious materials: past and future

Abstract: Rapid screening tests for supplementary cementitious materials (SCMs) have been in use for over 150 years. Over the years a multitude of methods have been put forward to predict the strength development of SCM blended mortars and concrete. This paper summarizes and rationalizes the main approaches and then applies them to a selection of materials that cover a broad range of SCMs, both pozzolanic and hydraulic. Included are siliceous fly ash, blast furnace slag, natural pozzolan, metakaolin and an inert quartz filler. The selected test methods are the Chapelle test, the Frattini test, active silica and alumina extractions, a dissolution rate test, and a new calorimetry-based test. The results are compared, interpreted and discussed in view of their aim of predicting the compressive strength development. Finally, a new test method is proposed that relates the cumulative heat of the SCM reaction in a simplified model system to the compressive strength development in standardized mortars. The new method is practical, repeatable and applicable to a wide range of SCMs (both pozzolanic and hydraulic), it furthermore reduces the experiment duration by a factor of 10 and correlates well to the compressive strength development of blended cement mortar bars.

Investigation on Soil–Geopolymer with Slag, Fly Ash and Their Blending

Abstract: Ground granulated blast furnace slag (GGBS)-based geopolymer is an excellent binder that attains high strength by curing at room temperature. Fly ash-based geopolymer binder, on the other hand, attains high strength when heated in particular temperature range. Although literatures on GGBS- and fly ash-based geopolymer are plenty, reported literatures on soil–geopolymer system are limited. An attempt has therefore been made in the present paper to investigate soil–geopolymer incorporating slag, fly ash and blending of slag and fly ash as source materials. It was observed that unconfined compressive strength of soil–geopolymer system increases with the source material content. Molar concentration of alkali activator, alkali-to-source material ratio and percent content of source material altogether affect the unconfined compressive strength of stabilized soil that is not straightforward. Na/Al and Si/Al ratios of the geopolymer mix ultimately govern the strength of stabilized soil. It was also observed that slag content is the most dominating factor affecting unconfined compressive strength rather than Na/Al ratio in case blending of GGBS and fly ash.