Rafat Siddique

Effect of fine aggregate replacement with Class F fly ash on the mechanical properties of concrete

This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (sand) was partially replaced with Class F fly ash. Fine aggregate (sand) was replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of Class F fly ash by weight. Tests were performed for properties of fresh concrete. Compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were determined at 7, 14, 28, 56, 91, and 365 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of fine aggregate (sand), and can be effectively used in structural concrete. D 2002 Elsevier Science Ltd. All rights reserved.

EFFECT OF FINE AGGREGATE REPLACEMENT WITH CLASS F FLY ASH ON THE ABRASION RESISTANCE OF CONCRETE

Abstract This paper presents the abrasion resistance of concrete proportioned to have four levels of fine aggregate replacement (10%, 20%, 30%, and 40%) with Class F fly ash. A control mixture with ordinary Portland cement was designed to have 28 days compressive strength of 26 MPa. Specimens were subjected to abrasion testing in accordance with Indian Standard Specifications (IS: 1237). Tests were also performed for fresh concrete properties and compressive strength. Tests on compressive strength and abrasion were performed up to 365 days. Test results indicated that abrasion resistance and compressive strength of concrete mixtures increased with the increase in percentage of fine aggregate replacement with fly ash. Abrasion resistance of concrete was improved approximately by 40% over control mixture with 40% replacement of fine aggregate with fly ash, and concrete with fine aggregate replacement could be suitably used.

PRECAST CONCRETE PRODUCTS USING INDUSTRIAL BY-PRODUCTS

This work aimed to help establish the use of high volumes of fly ash, bottom ash, and used foundry sand in manufacture of precast molded concrete products such as wet-cast concrete bricks and paving stones. ASTM Class F fly ash was used as a partial replacement for 0 (reference), 25, and 35% of portland cement. Bottom ash combined with used foundry sand replaced 0, 50, and 70% of natural sand. Tests for compressive strength, freeze-thaw resistance, drying shrinkage, and abrasion resistance were conducted on the wet-cast concrete masonry units manufactured at a commercial manufacturing plant. It was concluded that all wet-cast bricks could be used for both exterior and interior walls in regions where freezing and thawing is not a concern, and for interior walls in regions where freezing and thawing is a concern. No wet-cast paving-stone mixtures, including the reference mixture, met all ASTM requirements for paving stones.

Calcium carbonate precipitation by different bacterial strains

Bacteria are capable of performing metabolic activities which thereby promote precipitation of calcium carbonate in the form of calcite. In this study, it is shown that microbial mineral precipitation was a result of metabolic activities of some specific microorganisms. Concrete microorganisms were used to improve the overall behavior of concrete. It was predicted that bacterial calcium carbonate (CaCO 3) precipitation occurs as a byproduct of common metabolic processes such as urea hydrolysis. In this study, ureolytic bacteria that were capable of precipitating calcium carbonate were isolated and further their urease activity was tested based on the production of urease. Scanning electron microscopy (SED) analysis revealed the direct involvement of these isolates in calcium carbonate precipitation. The production of calcite was further confirmed by x-ray diffraction (XRD) and energy-dispersive x-ray (EDX) analysis.

Long-Term Performance of High-Volume Fly Ash Concrete Pavements

This investigation was undertaken to evaluate the long-term performance of concrete pavements made with high volumes of Class F and Class C fly ash (FA). Six different mixtures, three mixtures with Class C fly ash up to 70% cement replacement and three mixtures with Class F fly ash up to 60% cement replacement, were used. Long-term performance tests were conducted for compressive strength, resistance to chloride-ion penetration, and density using specimens from in-situ pavements. Long-term results showed greater pozzolanic strength contribution of Class F fly ash relative to Class C fly ash. Generally, based upon long-term data, mixtures containing Class F fly ash exhibited higher resistance to chloride-ion penetration relative to mixtures containing Class C fly ash. Compressive strengths of core specimens taken from in-situ pavements ranged from 45 to 57 MPa (6,600 to 8,300 psi) at seven to 14 years of age. The highest long-term compressive strength (57 MPa, 8,300 psi) was achieved for the high-volume fly ash mixture incorporating 67% Class F fly ash at the age of 7 years. Visual observations (in 2000) revealed that the pavement sections containing high volumes of Class F fly ash (40 to 67% FA) performed well in the field with only minor surface scaling. All other pavement sections have experienced very little surface damage due to the scaling.

Prediction of compressive strength of self-compacting concrete containing bottom ash using artificial neural networks

The paper presents a comparative performance of the models developed to predict 28days compressive strengths using neural network techniques for data taken from literature (ANN-I) and data developed experimentally for SCC containing bottom ash as partial replacement of fine aggregates (ANN-II). The data used in the models are arranged in the format of six and eight input parameters that cover the contents of cement, sand, coarse aggregate, fly ash as partial replacement of cement, bottom ash as partial replacement of sand, water and water/powder ratio, superplasticizer dosage and an output parameter that is 28-days compressive strength and compressive strengths at 7days, 28days, 90days and 365days, respectively for ANN-I and ANN-II. The importance of different input parameters is also given for predicting the strengths at various ages using neural network. The model developed from literature data could be easily extended to the experimental data, with bottom ash as partial replacement of sand with some modifications.

PROPERTIES OF CONCRETE INCORPORATING HIGH VOLUMES OF CLASS F FLY ASH AND SAN FIBERS

Abstract The results of an experimental investigation to study the effects of replacement of cement (by mass) with three percentages of fly ash and the effects of addition of natural san fibers on the slump, Vebe time, compressive strength, splitting tensile strength, flexural strength and impact strength of fly ash concrete are presented. San fibers belong to the category of “natural bast fibers.” It is also known as “sunn hemp.” Its scientific (botanical) name is Crotalaria juncea . It is mostly grown in the Indian subcontinent, Brazil, eastern and southern Africa and some parts of the United States (Hawaii and Florida). A control mixture of proportions 1:1.4:2.19 with W/Cm of 0.47 and superplasticizer/cementitious ratio of 0.015 was designed. Cement was replaced with three percentages (35%, 45% and 55%) of class F fly ash. Three percentages of san fibers (0.25%, 0.50% and 0.75%) having 25-mm length were used. The test results indicated that the replacement of cement with fly ash increased the workability (slump and Vebe time), decreased compressive strength, splitting tensile strength and flexural strength and had no significant effect on the impact strength of plain (control) concrete. Addition of san fibers reduced the workability, did not significantly affect the compressive strength, increased the splitting tensile strength and flexural strength and tremendously enhanced the impact strength of fly ash concrete as the percentage of fibers increased.

Ground Granulated Blast Furnace Slag

Ground granulated blast furnace slag (GGBS) is a by-product from the blast-furnaces used to make iron. Blast-furnaces are fed with controlled mixture of iron-ore, coke and limestone, and operated at a temperature of about 1,500°C. When iron-ore, coke and limestone melt in the blast furnace, two products are produced—molten iron, and molten slag. The molten slag is lighter and floats on the top of the molten iron. The molten slag comprises mostly silicates and alumina from the original iron ore, combined with some oxides from the limestone. The process of granulating the slag involves cooling of molten slag through high-pressure water jets. This rapidly quenches the slag and forms granular particles generally not bigger than 5 mm. The rapid cooling prevents the formation of larger crystals, and the resulting granular material comprises around 95% non-crystalline calcium-aluminosilicates. The granulated slag is further processed by drying and then grinding in a rotating ball mill to a very fine powder, which is GGBS.

Mechanical and durability properties of self-compacting concrete containing fly ash and bottom ash

The paper investigates the production of self-compacting concrete (SCC) more affordable for construction industry with various percentages of fly ash as part of the total powder content and bottom ash as replacement of fine aggregates. Various properties studied included strength (compressive and split tensile strength) and durability properties (carbonation and deicing salt surface scaling). Based on the materials used in this study, the SCC was observed to be flowable, cohesive, and developed 28-day compressive strength, approximately in the range of 18–35 MPa. Besides the environmental benefits, there could be some technical and economical advantages as well. As a general result, presence of fly ash and bottom ash affected the durability properties of concrete positively.

Rice Husk Ash

Rice husk ash (RHA) is generated by burning rice husk. On burning, cellulose and lignin are removed leaving behind silica ash. The controlled temperature and environment of burning yields better quality of rice-husk ash as its particle size and specific surface area are dependent on burning condition. The ash produced by controlled burning of the rice husk between 550°C and 700°C incinerating temperature for 1 h transforms the silica content of the ash into amorphous phase. The reactivity of amorphous silica is directly proportional to the specific surface area of ash. The ash so produced is pulverized or ground to required fineness and mixed with cement to produce blended cement.