Husain Al-Khaiat

Effect of initial curing on early strength and physical properties of a lightweight concrete

A 50 MPa 28-day cube compressive strength structural lightweight concrete of a fresh concrete density of 1800 kg/m3 was produced using Lytag coarse and fine aggregate. The long-term strength development and the durability characteristics of this lightweight concrete are being monitored in both the severe hot and dry and hot-coastal and salt-laden exposure conditions prevalent in Kuwait. The early results of the investigation suggest that the compressive strength of this concrete is less sensitive to lack of initial curing. However, depth of water penetration, which is indicative of the concrete’s permeability and hence durability, has been found to be more sensitive to the duration of initial curing even for the specimens exposed to the high-humidity seaside ambient conditions. The drying shrinkage of this concrete has been found to be more than 600 microstrain in the first 3 months’ duration. Longer term durability data will be reported in due course.

Strength and durability of lightweight concrete

Two lightweight aggregate concretes, SLWC35 and SLWC50, of 35 and 50 MPa 28 day cube compressive strength were cast. The concrete specimens made with lightweight coarse aggregates and a dune sand were continuously cured in water for one or 7 days and then exposed to predominantly hot and humid seaside ambient conditions containing air-borne salts. After 7 days of initial curing and on subsequent exposure to hot and humid air both SLWCs attained an almost similar strength to those continuously water cured cubes at an age of 12 months. In contrast, the water penetrability of SLWC35 and SLWC50 after 7 days of initial curing and subsequent exposure to the sea side was about 2 and 1.8 times the water penetration of those slabs which were water cured for the entire duration of 12 months. However, the depth of carbonation of the two sand lightweight concretes up to an age of 12 months were negligibly small. The results suggest that compressive strength is comparatively less sensitive to the curing regimes investigated. Both the chloride and sulphate penetration after 12 months exposure were found to be within tolerable limits. Also replacement of lightweight fine aggregate with normal weight sand produces a concrete that is somewhat more durable as indicated by their water penetrability and depth of carbonation when concretes are of equal strength.

Performance of epoxy-repaired concrete in a marine environment

The use of epoxy resins is becoming the most common method of concrete repair and rehabilitation. The performance of epoxy-repaired concrete in a marine environment has been investigated. Specimens were cast using two different types of cement, ordinary and sulphate-resistant Portland cement, damaged and then repaired using three different types of epoxy resins available in the Kuwaiti market. Specimens were then hung in the Arabian Gulf, in the tidal zone, so that they were subjected to cycles of wetting and drying for different time durations up to 18 months. The specimens were then tested in split and in slant shear to determine their tensile and bond strength. Results are compared with those of the control specimens, which were kept in a laboratory under controlled conditions.

Long-term strength development of concrete in arid conditions

Abstract A long-term investigation into the development of the compressive strength of various concretes, subjected to Kuwait hot and arid environmental conditions is reported. The main parameters investigated included, w/c ratio, cement type and content, and admixture type and its dosage. Other parameters investigated included the effects of using different water curing periods, curing compounds, and casting season. Forty-seven different mixes were placed on the roof of the laboratory building and were exposed to the environment. Compression tests on 100 mm cubes were carried out over a period in excess of five years. The results generally showed that the compressive strength of the concrete increased with age. The gain in strength at 1800 days above that at 28 days varied considerably depending on the concrete constituents and curing procedure. Concretes made with white Portland cement achieved higher compressive strengths than those made with ordinary or sulphate resisting Portland cements. Also, the type and dosage of admixture influenced the compressive strength of concrete. An increase in the water-curing period was more effective in improving the 28-day compressive strength than the 1800-day strength. The use of curing compounds or silica fume appeared to influence the early age strength more than the long-term strength. Compression test results from selected mixes at the age of 10 years indicated that there was little or no increase in strength during the previous five years.

Effect of sea water on epoxy-repaired concrete

Abstract Due to the Gulf War and the harsh environment in Kuwait, many concrete structures have been damaged and consequently repaired using epoxy resins. Some of these repaired buildings are close to the Gulf waterfront and were therefore exposed to sea water. The effect of sea water, at different temperatures, on the epoxy-repaired concrete has been investigated. Two different types of cement, ordinary and sulphate resistant, three different types of epoxy resins available in Kuwait, and different time durations of exposure to sea water at different temperature stations, were investigated. The effect of weather has also been studied, by keeping specimens immersed in tanks full of sea water in the open air for different time durations. Control specimens were also kept in sea water tanks which were put in an oven for different time durations and temperatures. Specimens were tested in compression, tension, flexure and shearbond. The results presented should help in understanding the expected behavior of epoxy-repaired concrete in Kuwait and other similar marine environments.

Analysis of Plates on an Elastic Foundation by the Initial Value Method

ABSTRACT The initial value method is applied to develop approximate solutions of rectangular plates on elastic foundations. The method consists of solving the governing differential equation of plates by a step-by-step integration procedure. A Winkler-type foundation is assumed in the analysis. A dimensionless quantity K that relates some characteristics of the plate to the foundation is introduced. The maximum values of deflections, moments, and shears are expressed in terms of the lateral load, dimensions of the plate, plate stiffness, and numerical factors. The values of these numerical factors for various values of the plates aspect ratio and K are given in tabular form. Only rectangular plates with uniformly distributed transverse loads and with Poissons ratio v= 0.3 are discussed. Four different boundary conditions are considered in the analysis. For these cases, the initial value method gives solutions with a maximum error of 1.0% when the foundation is not present.

Analysis of plates by the initial-value method

Abstract The initial-value method, which is an approximate numerical method, is applied to the analysis of isotropic plates. The initial-value method consists of solving the governing differential equation of plates by an integration technique. The integration is carried in one direction, and the derivatives in the other direction are represented by finite-difference operators on the deflections. The results and efficiency of the method are compared to the results of classical, finite-difference and finite-element methods. A wide variety of plate problems is considered, which include plates with transverse loading, plates with in-plane loading and continuous plates. The initial-value method has the lowest magnitudes of errors for all the examples considered in this study. To obtain high precision for a plate problem, the initial-value method requires the solving of far fewer simultaneous equations than the finite-difference and the finite-element methods.

Analysis and design of guyed transmission towers : case study in Kuwait

Abstract Guyed towers are special nonlinear structures requiring special techniques for analysis and design. The various aspects of geometric nonlinearity are discussed and the energy search method is explained, which is an algorithm believed to be suitable for the analysis of guyed towers. A two-dimensional example tower is investigated which demonstrates the effect of prebuckling displacements on the resulting critical wind load. A three-dimensional 600-m guyed tower case study is also analysed and designed using ANSYS and STAAD-III computer packages. Certain modelling assumption techniques are introduced in order to be able to use the two packages effectively for the analysis and design of guyed towers. The effects of accidental guy rupture and temperature variation have been studied as well.

EVALUATING BUILDING MATERIALS USED IN KUWAIT

Abstract In Kuwait, it has been a common practice to base the choice of materials and constructional methods on initial cost considerations, and the use of efficient and durable materials for the severe environment of the country is given little or no attention. This has, inevitably, led to short service lives of buildings despite the high construction cost in kuwait. The study presented in this paper describes a procedure followed for evaluating the performances of different building materials. An evaluation of materials used in kuwait for the construction of external walls and roofs of buildings was carried out. The evaluation, in the form of a questionnaire, was based on eleven performance criteria (eg. serviceability, durability etc.), and was completed by different organisations (eg. consultants, clients etc.). The study is useful in documenting past experiences about the use of such materials, and should help engineers and clients in making better decisions on the choice of appropriate materials in the future.

Free vibration analysis of orthotropic plates by the initial value method

Abstract A modified method of the classical initial value technique is presented for the free vibration analysis of rectangular orthotropic plates. The method employs finite difference operators in one direction and uses integration in the other direction. The solutions are superimposed to satisfy the boundary conditions. A detailed discussion of the method is given. A comparative study is presented of the initial value method and other numerical methods. Three examples that show the accuracy of the method are presented.