Wasim Khaliq

Effect of Temperature on Thermal Properties of Different Types of High-Strength Concrete

The knowledge of high temperature thermal properties is critical for evaluating the fire response of concrete structures. This paper presents the effect of temperature on the thermal properties of different types of high-strength concrete (HSC). Specific heat, thermal conductivity, and thermal expansion are measured for three concrete types, namely, HSC, self-consolidating concrete (SCC), and fly ash concrete (FAC), in the temperature range from 20–800°C. The effect of steel, polypropylene, and hybrid fibers on thermal properties of HSC and SCC is also investigated. Results from experiments show that SCC possesses higher thermal conductivity, specific heat, and thermal expansion than HSC and FAC in the 20–800°C temperature range. Data generated from tests is utilized to develop simplified relationships for expressing different thermal properties as a function of temperature. The proposed thermal property relationships can be used as input data for evaluating the response of concrete structures under fire conditions.

Effect of Temperature on Thermal and Mechanical Properties of Steel Bolts

AbstractWhen steel-framed structures are exposed to fire, connections play a crucial role in transferring forces from highly stressed members to less stressed members. The performance of bolted connections, under ambient and fire conditions, depends on the strength characteristics of bolts. At present, the fire resistance of bolts is evaluated by assuming the high-temperature properties to be same as those of conventional mild steel. This is due to lack of data on high-temperature properties specific to high-strength steel bolts. To overcome this drawback, high-temperature thermal and mechanical properties of Grade A325 and A490 high-strength steel bolts are evaluated. Thermal conductivity and specific heat of A325 and A490 were measured in the temperature range 20–735°C, whereas thermal expansion was measured in the range 20–1000°C in both the heating and cooling phases of fire. Steady-state single shear and tension tests were carried out on A325 and A490 bolts at 20–800°C. Results from these tests were ...

High Temperature Mechanical Properties of High-Strength Fly Ash Concrete with and without Fibers

There is an increasing interest in the use of high-strength fly ash concrete (HFAC) due to growing environmental awareness. Knowledge of high temperature material properties is critical for evaluating the fire response of structures. This paper presents the effect of temperature on mechanical properties of plain HFAC and polypropylene fiber-reinforced HFAC (HFAC-P) with a compressive strength of approximately 70 MPa (10.1 ksi). A series of strength tests were carried out to evaluate compressive strength, tensile strength, stress-strain response, and elastic modulus of HFAC and HFAC-P in a 20 to 800°C (68 to 1472°F) temperature range. Results from mechanical property tests indicate that both HFAC and HFAC-P experience significant degradation in compressive and tensile strength, and elastic modulus with temperature. Data generated from tests are used to develop simplified relations for expressing strength and elastic modulus of HFAC and HFAC-P as a function of temperature. The proposed relations can be used as input data in computer models for evaluating fire response of structures made of HFAC with and without fibers.

Immobilization in cement mortar of chromium removed from water using titania nanoparticles

Because of the high toxicity of chromium, particularly as Cr (VI), it is removed from industrial effluents before their discharge into water bodies by a variety of techniques, including adsorption. Ultimate disposal of the sludge or the adsorbate, however, is a serious problem. While titania, in nanoparticle form, serves as a very good adsorbent for chromium, as an additive, it also helps to increase the compressive strength of mortar and concrete. Combining these two properties of the material, titania nanoparticles were used to adsorb chromium and then added to mortar up to a concentration of 20% by weight. The compressive strength of the resulting mortar specimens that replaced 15% of cement with chromium laden titania showed an improved strength than that without titania, thus confirming that this material had positive effect on the mortar strength. Leachate tests using the Toxicity Characteristics Leaching Procedure (TCLP) confirmed that the mortar sample chromium leachate was well within the permissible limits. The proposed technique thus offers a safe and viable method for the ultimate disposal of toxic metal wastes, in general, and those laden waste chromium, in particular.

Effectiveness of Polypropylene and Steel Fibers in Enhancing Fire Resistance of High-Strength Concrete Columns

AbstractFire-induced spalling is one of the concerns with the use of high-strength concrete (HSC) in structural applications. Some recent studies have recommended addition of polypropylene and/or s...

RETRACTED CHAPTER: High Temperature Thermal Properties of Vanadium Steel

When steel framed structures are exposed to fire, the thermal response of steel plays a crucial role in determining fire resistance (FR). Due to changing thermal properties with temperature, the strength and stiffness of steel is lost at a greater rate under elevated temperatures as compared to concrete and wood. With the recent research and development, significant improvement in strength properties has been achieved and new types of steel such as vanadium steel have come to the construction industry. For FR evaluation, high temperature (HT) properties specific to vanadium steel are to be known. These properties vary with temperature and the composition (type) of steel. For vanadium steel, three thermal properties, namely thermal conductivity, specific heat, and thermal expansion were measured in 20-750°C (20-1000°C for thermal expansion) using state-of-the-art test equipment. For comparison purpose, conventional steel namely A36 was also considered in the test program. Using the data generated from the thermal property tests, HT property relations for vanadium steel are proposed as a function of temperature. The use of these HT property relations, developed specific to vanadium steel can lead to realistic assessment of FR of structural members made of vanadium steel.

Characterization of Conventional and Modern Curing Techniques in Concrete

Appropriate curing of concrete is of vital importance in development of desired material properties in concrete namely compressive strength, durability, and dense uniform microstructure. Improper and intermittent curing is considered as one of the major reasons for concrete failures as evident in the form of cracks that consequently lead to durability issues of structures. An experimental program was designed to study the behavior of concrete under various conventional and modern curing techniques. Numerous cylindrical specimens were tested with different conventional and modern curing techniques to quantify their effects on curing of concrete. Microstructural and compressive strength development analyses at different ages were conducted to monitor the effect of curing methods. This work is helpful in establishing the best curing techniques for attainment of compressive strength and durability in concrete.

Energy efficient design and sustainable buildings

The use of energy in buildings and infrastructure has increased many folds suggesting that alternate means must be devised to conserve energy and operate the buildings with sustainable means. For the buildings, energy efficiency can be achieved using the insulation materials, improved architectural technique, and modified construction methodology. Energy demand to operate buildings must be reduced to develop energy efficient and sustainable buildings for the future, without compromising the living comfort, performance, and services. The architecture, design, and orientation of building are altered to introduce energy efficient and sustainable design in commercial, residential, and industrial buildings. Observations and experiments were carried out on four existing buildings and a model was studied and compared based on orientation, construction materials used, type of construction, and architectural techniques. The results show that, using Alpolic Cladding and double layered windows at outer face of buildings gives 8% more thermal efficiency than the ordinary construction. The cavity wall construction enhances the energy conservation of the building by 6% as compared to traditional construction of block masonry. The model studies show that using cavity wall and Structural Concrete Insulated Panel (SCIP) as cladding/infill walls in frame structures can reduce the energy demand of the building upto 3%. Building orientation, architecture, use of latest energy efficient materials, and enhanced construction techniques contribute significantly towards energy efficient performance of buildings.