Shiw S. Singh

MECHANICAL PROPERTIES AND DURABILITY OF CONCRETE MADE WITH BLENDED FLY ASH

This study focused on evaluating the effects of blended fly ash on mechanical properties and durability of concrete. In this investigation two reference mixtures were used. One was a mixture without fly ash, and the other contained 35% ASTM Class C fly ash. Additional mixtures were composed of three blends of ASTM Class C and Class F fly ash while maintaining a total fly ash content of 40% of the total cementitious materials. Mechanical properties such as compressive strength, tensile strength, flexural strength, and modulus of elasticity were determined. Durability related properties determined were drying shrinkage, abrasion resistance, salt scaling resistance, and electrical prediction of chloride ion penetration. The results showed that blending of Class C fly ash with Class F fly ash showed either comparable or better results than either the reference mixture without fly ash or the unblended Class C fly ash. Blending of fly ash, therefore, leads to comparable or better quality and reduced cost, attributed to the use of Class F versus Class C fly ash in concrete.

Use of post-consumer waste plastics in cement-based composites

Abstract This paper describes an innovative use of post-consumer waste HDPE plastic in concrete as a soft filler. A reference concrete was proportioned to have the 28-day compressive strength of 5000 psi (35MPa). A high-density plastic was shredded into small particles for use in the concrete. These particles were subjected to three chemical treatments (water, bleach, bleach + NaOH) to improve their bonding with the cementitious matrix. The plastic particles were added to the concrete in the range of 0–5% of total mixture by weight. Compressive strengths were measured for each test mixture. The results showed that chemical treatment has a significant effect on performance of the plastic filler in concrete. Of the three treatments used on the plastic, the best performance was observed with the alkaline bleach treatment (bleach + NaOH) with respect to compressive strength of concrete.

Permeability of concrete containing large amounts of fly ash

Abstract This study was carried out to evaluate the influence of addition of a Class C fly ash on concrete permeability. An air entrained reference concrete mixture without fly ash was proportioned to have a 28-day strength of 41 MPa. Concrete mixtures were also proportioned to have cement replacement with fly ash in the range of 0–70% by weight. For each concrete mixture, compressive strength, chloride permeability, air permeability, and water permeability were determined. Air and water permeability were evaluated by using the Figg method. Chloride permeability of the concrete was measured in accordance with the ASTM C 1202. At ages up to 28-day, no-fly ash concrete attained lower air permeability compared to high-volume fly ash concretes. At 91 days, the mixture having 50% cement replacement exhibited the lowest air permeability. The same was true for water permeability also. In general, addition of fly ash caused a decrease in chloride permeability of concrete up to 50% cement replacement.

INFLUENCE OF FLY ASH ON SETTING AND HARDENING CHARACTERISTICS OF CONCRETE SYSTEMS

This project was carried out to investigate the effect of fly ash obtained from various sources. A reference mixture without fly ash was proportioned to have 28-day design strength of 35 MPa. Fly-ash mixtures were proportioned to contain fly ash in the range of 0 to 100 percent by mass of the cementitious medium. The ratio of fly ash to cement was kept at about 1.25. In general, initial and final times of setting of concretes were greatly affected by both source and fly ash content. The times of setting were generally delayed up to a certain level of cement replacement with fly ash. Beyond this level, which was about 60%, rapid setting occurred.

APPLICATION OF FOUNDRY BY-PRODUCT MATERIALS IN MANUFACTURE OF CONCRETE AND MASONRY PRODUCTS

This research was initiated to evaluate the performance of foundry by-products in concrete and masonry products. Two series of experiments were conducted. The first series of experiments were directed toward the use of an air-cooled foundry slag in concrete as a partial replacement of coarse aggregate. The second series involved the use of foundry sand as a partial replacement of fine aggregate for making masonry blocks and paving stones. In the first series, foundry slag concrete was tested under laboratory conditions. A reference concrete without foundry slag was proportioned to obtain a 28-day compressive strength of 41 MPa. Two other mixes containing 50 and 100 percent foundry slag as a replacement of regular aggregate were also proportioned. The 100 percent slag mix showed compressive strength comparable to the reference mix. However, the modulus of elasticity of concrete containing 100 percent slag was higher than the reference concrete. Four mixes with and without foundry sands were proportioned for the manufacture of masonry blocks with a design strength of 10 MPa at the 28-day age. In addition, four mixes--three with and one without foundry sands--were also proportioned for the manufacture of paving stones with a design strength of 55 MPa at the 28-day age. In all of the mixes, 35 percent regular sand was replaced with new/used foundry sand obtained from different sources; no admixtures were added to the mixes. Test results indicated that masonry blocks made with 35 percent used foundry sand passed the American Society for Testing and Materials (ASTM) requirements for compressive strength, absorption, and bulk density. However, the paving mixes used in this study did not meet the target strength of 55 MPa and showed slightly higher absorption than the ASTM limit for paving stones.

Abrasion resistance of concrete as influenced by inclusion of fly ash

Abstract This research was conducted to evaluate abrasion resistance of high-volume fly ash concrete. A reference plain portland cement concrete was proportioned to obtain 28-day strength of 41 MPa. Concrete mixtures were also proportioned to have two levels of cement replacements (50 and 70%) with an ASTM Class C fly ash. Abrasion tests were carried out using the rotating cutter method as per ASTM C-944. In this work all the concrete specimens made either with or without fly ash passed the abrasion resistance requirements per ASTM C-779, Procedure B. An accelerated test method was also developed to evaluate abrasion resistance of concrete. This method used the rotary cutter device having dressing wheels equipped with smaller size washers. A measured amount of standard Ottawa sand was added to the surface being abraded at one minute intervals. The accelerated test results exhibited lower abrasion resistance for high-volume fly ash concrete systems relative to no-fly ash concrete.

Properties of high performance concrete systems incorporating large amounts of high-lime fly ash

Abstract This research was undertaken to evaluate the engineering properties of high-lime (ASTM Class C) fly ash concretes. An air-entrained reference concrete mixture without fly ash was proportioned to have 28-day compressive strength of 41 MPa. Additionally, concrete mixtures were also proportioned to have cement replacement with Class C fly ash in the range of 0–70% by weight. For each concrete mixture, specimens were made to evaluate compressive strength, tensile strength, flexural strength, modulus of elasticity, shrinkage, abrasion resistance, air permeability, water permeability, chloride ion permeability, air-void parameters, freezing and thawing durability, and salt scaling resistance, of hardened concrete. The results of this study established that high-performance concrete incorporating Class C fly ash at 30% cement replacement can be proportioned for high-strength applications. In general, concrete mixtures up to 50% cement replacement with fly ash showed satisfactory performance with respect to strength and physical durability properties appropriate for structural applications.

Enhancement in mechanical properties of concrete due to blended ash

This study was carried out to evaluate the effects of blended ash mixture on mechanical properties of concrete. In this study two reference mixtures were used. One of the mixtures was a no-fly ash mixture, and the other mixture contained 35% unblended Class C fly ash. Additional mixtures were composed of three blends of Class C and Class F fly ash while maintaining a total fly ash content of 40% of the total cementitious materials. Mechanical properties such as compressive strength, tensile strength, flexural strength, and modulus of elasticity were determined as a function of age ranging from 1 to 91 days. The results showed that blending of Class F fly ash with Class C fly ash showed either comparable or better results compared to either the reference mixture without fly ash or the unblended Class C fly ash concrete mixture at a fly ash concentration of 40% of total cementitious materials.

Fatigue Property of Concrete With and Without Mineral Admixtures

A number of studies have shown that concrete fatigue strength is significantly influenced by a large number of variables including stress range, rate of loading, load history, stress reversal, rest period, stress gradient, material properties, etc. Effects of these parameters on fatigue characteristics of concrete are addressed in this paper. In general, endurance or fatigue flexural limit of plain concrete was found to vary between approximately 50 and 70% of its static flexural strength. But it can be lower than 50% when concrete is tested in water.

Time of Setting Influenced by Inclusion of Fly Ash and Chemical Admixtures

This investigation was performed to establish the effects of pozzolanic and chemical admixtures on setting behavior of cement paste at normal consistency. An ASTM Class C fly ash was used as a pozzolanic and cementitious admixture. Mixtures were proportioned to contain fly ash in the range of 0-100% by mass of the cementitious materials using a cement replaced by fly ash in a proportion of 1:1.25. One source of ASTM Type I cement was used. The effects of five admixtures, air-entraining agent, water reducer, retarder, high-range water-reducer, and hemihydrate gypsum on setting times remained essentially the same or were slightly delayed up to 20% cement replacement with respect to the 0% fly ash mixture. Beyond this range, the times of setting were generally accelerated. Increased rate of setting occurred at cement replacement levels of 40% and above, irrespective of type of chemical admixtures used.