Khandaker M. Anwar Hossain

DEVELOPMENT OF COST-EFFECTIVE SELF-CONSOLIDATING CONCRETE INCORPORATING FLY ASH, SLAG CEMENT, OR VISCOSITY-MODIFYING ADMIXTURES

The concept of self-consolidating concrete (SCC) as a building material has gained worldwide acceptance in recent years. The development of a cost-effective SCC with desirable fresh and hardened properties is important for such concrete to be used in structural construction in the future. SCC can be manufactured by incorporating either supplementary cementitious materials such as fly ash and slag cement, or viscosity-modifying agents (VMAs). Commercially available VMAs are expensive, making it important to explore new cost-effective VMAs to manufacture more economical SCC. This paper compares the performance of SCCs incorporating fly ash, slag cement, and VMAs based on fresh and mechanical properties. The feasibility of manufacturing such an SCC is assessed based on cost analysis. Results indicate that an economical SCC with the desired properties could be successfully developed by the incorporation of fly ash, slag cement, or VMA.

BLENDED CEMENT USING VOLCANIC ASH AND PUMICE

Abstract This paper reports the results of investigation to assess the suitability of volcanic ash (VA) and pumice powder (VPP) for blended cement production. Tests were conducted on cement where Portland cement (PC) was replaced by VA and VPP within the range of 0 to 50%. The physical and chemical properties of VA and VPP were critically reviewed to evaluate the possible influences on cement properties. The investigation included testing on both fresh and hardened states of cement paste. The standard tests conducted on different PC–VA and –VPP mixtures provided encouraging results, comparable to those for fly ash (FA) cement, and showed good potential of manufacturing blended Portland volcanic ash cement (PVAC) and Portland volcanic pumice cement (PVPC) with higher setting time and low heat of hydration using up to 20% replacement.

Influence of Aggregate Type and Size on Ductility and Mechanical Properties of Engineered Cementitious Composites

The influence of aggregate type and size on engineered cementitious composite (ECC) mechanical and ductility properties was investigated and the results presented in this paper. A micromechanically-based high-performance fiber-reinforced cementitious composite, ECC enjoys improved durability and high ductility due to tight crack width. Microsilica sand (200 μm [0.008 in.] maximum aggregate size) is typically used to produce standard ECC mixtures. There was investigation of ECC mixtures containing either gravel sand or crushed dolomitic limestone sand with maximum sizes of 2.38 or 1.19 mm (0.094 or 0.047 in.) in this study. Three different ECC mixtures with 1.2, 2.2, and 4.2 fly ash/portland cement (FA/C) ratios were cast for each aggregate type and maximum aggregate size. There was experimental determination of crack development, drying shrinkage behavior, and the effects of FA/C, aggregate type, and maximum aggregate size on compressive, flexure, and unixial tensile properties. Experimental results show that strain-hardening behavior with strain capacities, provided that the matrix employs a high FA content, can be compared with the standard microsilica sand ECC mixtures, in ECC mixtures produced with gravel sand and crushed dolomitic limestone sand with higher maximum aggregate sizes. Tensile strengths of these mixtures can be 3.57 to 5.13 MPAa (0.52 to 0.74 ksi), and tensile ductility can maintain, at 28 days of age, 1.96 to 3.23%. Material behavior can be further improved by using crushed dolomitic limestone sand and gravel sand, since they can be drying-shrinkage arrestors in the paste.

DEVELOPMENT OF STATISTICAL MODELS FOR MIXTURE DESIGN OF HIGH-VOLUME FLY ASH SELF-CONSOLIDATING CONCRETE

Self-consolidating concrete (SCC) in the fresh state is known for its excellent deformability, high resistance to segregation, and use, without applying vibration, in congested reinforced concrete structures characterized by difficult casting conditions. Such concrete can be obtained by incorporating either mineral admixtures such as fly ash (FA) or viscosity-modifying admixtures (VMA). The use of VMA has proven very effective in stabilizing rheology of SCC, and recent research has focused on development of new, cheaper VMAs compared with currently available, costly commercial ones. Research to produce an economical SCC with desired properties has been conducted in recent years into the use of FA. In this paper, 21 statistically balanced concrete mixtures were investigated to minimize the use of high-range water-reducing admixtures (HRWRA) and to optimize the use of fly ash in SCC. The minimum use of HRWRA and optimum use of FA were desired in this study. Four independent variables were used for design of SCC mixtures. The fresh concrete properties were determined from slump flow, V-funnel flow, filling capacity, bleeding, air content, and segregation tests. The mechanical properties and durability characteristics of SCC such as compressive strength, freezing/thawing resistance, rapid chloride permeability, surface scaling resistance, and drying shrinkage were determined to evaluate the performance of SCC. Four statistical models to predict the slump flow, 1- and 28-day compressive strength, and the rapid chloride permeability of SCC were developed and their performances were validated.

Mixture Design, Strength, Durability, and Fire Resistance of Lightweight Pumice Concrete

The authors discuss lightweight volcanic pumice concrete (VPC) development in which 21 concrete mixtures are illustrated through use of pumice as aggregate. The authors describe VPC mixture fresh, mechanical, and durability properties, including water permeability, drying shrinkage, modulus of elasticity, density, tensile strength, compressive strength, air content, and slump. The authors also describe the fire resistance of VPC subjected, for different durations (with a 2 hour maximum), to elevated temperatures (up to 800° C [1472° F]). The basis of performance judgment is VPC physical changes and residual strength compared with normal density concrete (NC). The investigation suggests for structural applications, VPC production having both durability characteristics and satisfactory strength. With the increase of fire and temperature duration, both NC and VPC strength is found to decrease. Compared with NC after elevated temperature exposure for different durations, VPC shows better strength retaining capacity and residual strength.

Development of Volcanic Ash Concrete: Strength, Durability, and Microstructural Investigations

This report investigates the possibility of using volcanic ash as a cement replacement material in concrete production. Comprehensive tests on the durability of volcanic concrete mixtures and the performance of fresh and hardened concrete properties were conducted. The concrete mixtures were assessed by slump, air content, and compressive strength. The durability characteristics studied were: rapid chloride permeability, drying shrinkage, water permeability, mercury intrusion porosimetry and differential scanning calorimetry tests. The development of acceptable strength and durable volcanic ash concrete that is inexpensive and environmentally friendly would be helpful for the rehabilitation of volcanic disaster areas and sustainable development.

Effect of Metakaolin and Silica Fume on Rheology of Self-Consolidating Concrete

The rheology of self-consolidating concrete (SCC) containing metakaolin (MK) versus silica fume (SF) was compared. Plastic viscosity and yield stress were evaluated at different slump-flow values using a concrete viscometer. The effects of high-range water-reducing admixture (HRWRA) dosage, the total time for flow, the time to reach 19.68 in. (500 mm) diameter (T50), and the final diameter of the slump-flow test, as well as the influence of the mixture viscosity on the flowability and passing ability were investigated. Plastic viscosity and yield stress increased with the increased percentage of MK, but not with that of SF. However, the yield value sharply increased with the increased percentage of SF. Good correlations between slump-flow diameter and yield stress, viscosity and T50, viscosity and total slump-flow time, as well as viscosity limits for SCC mixtures based on the mixture usage, construction requirements, and member characteristics were established.

Lightweight Concrete Incorporating Volcanic Ash-Based Blended Cement and Pumice Aggregate

This paper presents the workability, mechanical, durability, and microstructural properties of lightweight concrete (LWC) incorporating pumice aggregate, normal-weight gravel aggregate, ASTM type I portland cement, and volcanic ash (VA)–based ASTM Type I blended cement (PVAC). Workability and mechanical properties of LWC mixtures such as slump, air content, compressive strength, tensile strength, density, and modulus of elasticity are described. The durability and microstructural characteristics are investigated by drying shrinkage (DS), water permeability, mercury intrusion porosimetry (MIP), differential scanning calorimetry (DSC), and microhardness tests. The variables in the study include percent replacement (0, 50, 75, and 100% by volume) of coarse gravel aggregate (GA) by coarse volcanic pumice aggregate (VPA), water-to-binder ratio (W/B) by mass, aggregate-to-binder ratio (A/B) by mass, total binder content, and cement types (ASTM type I cement and PVAC). The investigation suggests the production o...

Methods to control efflorescence in alkali-activated cement-based materials

Efflorescence is an important issue in the development of alkali-activated or geopolymer binders. Severe efflorescence in these materials may even put their soundness and structural integrity at risk. The present chapter presents an outline of the general features of the phenomenon, including a definition of efflorescence, its effects and consequences, types of efflorescence and formation mechanism. After a brief literature survey on efflorescence formation in alkali-activated or geopolymer binders, the chapter focuses on methods to reduce efflorescence formation in alkali-activated or geopolymer binders, including careful adjustment of chemical composition of the material, application of curing conditions and utilization of special additives.

Pollutant dispersion characteristics in Dhaka city, Bangladesh

Air pollution is a major environmental concern in major cities around the world. The major causes of air pollution include rapid industrialization/urbanization and increased non environment-friendly energy production. This paper analyses the atmospheric pollutant such as carbon monoxide (CO) and particulate matter (PM) dispersion characteristics of Dhaka city. The yearly and diurnal variations of pollutant concentration are described by taking into consideration of both meteorological and emission source parameters highlighting washout effect due to rainfall and inversion phenomena. Concentration of PM (both PM2.5 and PM10) and CO in the ambient air are measured for a period of one year with Airmetric Minivol air samplers and Gas Chromatographic (GC) technique, respectively. The trend over the year shows an increase in the monthly average hourly PM and CO concentrations in winter months (November to March) when both PM10 and PM2.5 annual average concentrations (about 130 and 95 μg m−3, respectively) exhibit levels exceeding World Health Organization (WHO) guidelines as well as exceed more than twice the national standards of annual PM10 (50 μg m−3) and PM2.5 (15 μg m−3) concentrations. Such high pollutant concentrations may have significant health implications for residents of Dhaka city. It is also found that the PM concentration increases with the increase of wind speed during dry winter season and is also influenced by transboundary air pollution. The data and subsequent recommendations can be useful in formulating air quality management strategies for the Dhaka city.