Showing papers by "Payam Shafigh published in 2019"

Performance of High Strength Concrete Subjected to Elevated Temperatures: A Review

Abstract: Advancement in the field of construction has given rise to the modification of conventional materials in order to utilize the full potential of their components to achieve high durability, strength, and other engineering characteristics. Construction materials should ideally be environmental friendly. These diverse requirements resulted in the invention of high strength concrete (HSC). A rapidly increasing use of HSC in most of the construction projects has encouraged researchers to identify its behavior at elevated temperatures. This has led to the recognition of an inadequate understanding of elevated temperatures’ effects on the behavior of HSC. This paper initially provides necessary information about HSC and relates its benefits. A number of different design standards for the preparation of HSC are also presented and compared. Previous research activities performed on HSC to identify the effect of elevated temperatures on the properties of HSC are reviewed. Findings showed that the mechanical properties of NSC decreases at a 10% to 20% higher rate than HSC ranging between ambient temperature and approximately 350°C, depending upon the mix proportions and initial compressive strength of the concrete. The differences become narrower at temperature above 350°C. Major failure modes are identified and future recommendations are presented.

Production of high-strength lightweight concrete using waste lightweight oil-palm-boiler-clinker and limestone powder

Abstract: Oil-palm-boiler clinker (OPBC) is an agricultural solid waste from the incineration process of solid wastes in palm oil industry. The OPBC that is highly porous and lightweight in nature is suitabl...

Crossover effect in cement-based materials: A review

Abstract: Cement-based materials (CBMs) such as pastes, mortars and concretes are the most frequently used building materials in the present construction industry. Cement hydration, along with the resulting compressive strength in these materials, is dependent on curing temperature, methods and duration. A concrete subjected to an initial higher curing temperature undergoes accelerated hydration by resulting in non-uniform scattering of the hydration products and consequently creating a great porosity at later ages. This phenomenon is called crossover effect (COE). The COE may occur even at early ages between seven to 10 days for Portland cements with various mineral compositions. Compressive strength and other mechanical properties are important for the long life of concrete structures, so any reduction in these properties is of great concern to engineers. This study aims to review existing information on COE phenomenon in CBMs and provide recommendations for future research.

Comparative study of mechanical properties for substitution of normal weight coarse aggregate with oil-palm-boiler clinker and lightweight expanded clay aggregate concretes

Abstract: This paper deals with a comparatively study of the engineering properties of the Oil-palm-boiler clinker (OPBC) OPBC and lightweight expanded clay aggregate (LECA) concretes. A grade 70 normal-weight concrete was designed as control mix. Normal weight coarse aggregate was substituted with OPBC and LECA up to 100% by volume, respectively. Their properties — workability, density, compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, and water absorption — were studied. Results showed that at the same mix proportion, all mixes exhibited acceptable workability, except for concrete containing LECA up to 75% onwards, which required the reduction of superplastisizer dozen to 16%. Mixes with 75% onwards LECA content exhibited acceptable workability. The oven dry density of concrete containing 100% OPBC and 50% LECA onwards, respectively, in this study can be considered as lightweight concrete. The use of saturated OPBC and LECA in concrete improves the mechanical properties of concrete under air drying condition. The ceiling strength of LECA concrete is at the early age of 7 days, whereas it happens to normal weight concrete and OPBC concrete at a later age. The water absorption of all mixes is below 3%, which can be considered as good concrete.

An Experimental and Numerical Study on the Flexural Performance of Over-Reinforced Concrete Beam Strengthening with Bolted-Compression Steel Plates: Part II

Abstract: This study presents an experimental investigation and finite element modelling (FEM) of the behavior of over-reinforced simply-supported beams developed under compression with a bolt-compression steel plate (BCSP) system. This study aims to avoid brittle failure in the compression zone by improving the strength, strain, and energy absorption (EA) of the over-reinforced beam. The experimental program consists of a control beam (CB) and three BCSP beams. With a fixed steel plate length of 1100 mm, the thicknesses of the steel plates vary at the top section. The adopted plate thicknesses were 6 mm, 10 mm, and 15 mm, denoted as BCSP-6, BCSP-10, and BCSP-15, respectively. The bolt arrangement was used to implement the bonding behavior between the concrete and the steel plate when casting. These plates were tested under flexural-static loading (four-point bending). The load-deflection and EA of the beams were determined experimentally. It was observed that the load capacity of the BCSP beams was improved by an increase in plate thickness. The increase in load capacity ranged from 73.7% to 149% of the load capacity of the control beam. The EA was improved up to about 247.5% in comparison with the control beam. There was also an improvement in the crack patterns and failure modes. It was concluded that the developed system has a great effect on the parameters studied. Moreover, the prediction of the concrete failure characteristics by the FE models, using the ABAQUS software package, was comparable with the values determined via the experimental procedures. Hence, the FE models were proven to accurately predict the concrete failure characteristics.

Mechanical and Durability Properties of High Strength High Performance Concrete Incorporating Rice Husk Ash

Abstract: Nowadays, more infrastructure projects require concrete to have a high durability in addition to high strength. High strength high performance concrete (HSHPC) was developed to solve those problems. The weaknesses of HSHPC are high cost of constituent material such as silica fume which is mostly used as supplementary cementitious material (SCM), high cement content at low w/b, low workability and the need of specific curing regime. This research utilized rice husk ash (RHA) as the local waste material as an alternative to silica fume (SF). Five mixes of OPC concrete, 10%, 15% and 20% partial cement replacement by RHA, and 10% partial cement replacement by SF were chosen. The water/cementitious ratio adopted was 0.25 and the total cementitious materials content was 550 kg/m3. The mixing method adopted was the two-step mixing method. In addition to the development of compressive strength, workability, modulus of elasticity and the residue of compressive strength of concrete experienced immerse in 5% solution of magnesium sulphate were also reported. The specimens were cured and tested at 1, 3, 7, 28 and 56 days. Results show that concrete incorporating rice husk ash as 10% partial cement replacement and crushed granite as coarse aggregate with maximum size of 19 mm can achieve compressive strength as high as 110 MPa at 28 days under water curing regime. The HSHPC incorporating 10% RHA showed better overall performance than the HSHPC containing 10% silica fume and the control OPC.

Determination of optimum insulation and cement plaster thickness for bungalow buildings through a simulation-statistical approach using response surface methodology

Abstract: Insulating interior side of external wall and finishing by cement plaster is one of the most appropriate methods of reducing annual energy consumption in available buildings. The aim of this study is to determine the optimum expanded polystyrene (EPS) and cement plaster thickness for bungalow building in Malaysia. The present study evaluates the effect of different thermal insulation and interior cement plaster thicknesses on the annual cooling energy consumption. Furthermore, the optimum thickness of EPS and plaster is estimated based on wall type and building orientation. Two different types of walls made of concrete and brick are considered. EPS and plaster were used in the range of 20 to 100 mm and 0 to 20mm, respectively. The results show that both thermal insulation and plaster thickness have a direct effect on annual cooling energy consumption, however, the influence of wall thermal insulation thickness is more significant than cement plaster thickness. Further, the optimum EPS thickness decreases with the increment in cement plaster thickness for different orientations and wall types. The optimum EPS thickness ranges from 31.5 mm to 53.1 mm based on wall type, orientation and cement plaster thickness. Utilizing optimum EPS and cement plaster thicknesses can thus reduce annual energy consumption by about 6 to 12% in different directions.

High Strength Concrete Incorporating Oil-Palm-Boiler Clinker as Coarse Lightweight Aggregate

Abstract: Construction industry demands for high amount of raw material to produce concrete. The constant reduction of natural resources results in negative impact to the environment and lack of raw material. Promotion of utilization of agricultural wastes in production of concrete can minimize the environmental impact towards the sustainable development. In this study, the oil-palm-boiler clinker (OPBC) which is an agricultural waste from palm oil industry was used to substitute the crush granite in conventional concrete from 0 to 50% by volume in increments of 12.5%. Tests conducted in this study were compressive strength in different curing regimes, flexural strength and water absorption. The test results showed that concretes containing 37.5 to 50% OPBC can be categorized as semi-lightweight aggregate concrete with high strength. This aggregate has considerable potential for performing internal curing in concrete. Using OPBC in concrete reduced the flexural strength; however, the reduction was not significant. Although water absorption showed that concretes containing OPBC have slightly higher water absorption, however, all these concrete could be considered as good quality concrete.