No description available.

The disposal of waste tyres and steel fibres from tyres is a serious worldwide environmental problem. This thesis examines the use of steel fibres extracted from waste tyres as reinforcement for concrete. Previous attempts to use such fibres with concrete ended up in balling of the fibres and wasting of the concrete. Four concrete mixes using three different types of fibres (from shredded tyres, from pyrolysis and commercially available fibres) were developed. An optimisation procedure was used to maximise the amount of fibre used whilst maintaining a reasonable degree of workability. Single and double sided pull-out tests were developed to determine the anchoring characteristics of fibres. Double-sided tests with multi-fibres were found to be the most reliable. The anchoring characteristics of tyre fibres were found to be as good as for commercially available fibres. Critical fibres lengths were determined for the different fibres used. A simple fibre pull-out model is proposed. Flexural toughness tests were developed and optimised based on the ASTM and Japanese standards. The crack development, neutral axis depth and characteristic length were examined in detail. An examination of the RILEM 0-£ model has shown that the model can overestimate the flexural capacity of Steel Fibre Reinforced Concrete (FRC). New 0-£ models were derived by adopting inverse analysis techniques on results from flexural tests on notched beams. These models when used with Finite Element Analysis (FEA) can predict the behaviour of the tested prisms accurately. For design purposes the models have been simplified. Parametric studies led to design equations which predict the design moment by using a fibre parameter (relating to length and bond) and the fibre amount by weight. The design equations are applied in several applications including the design of slabs on grade. The results compare favourably with existing design guidelines. Finally, slabs for drainage covers were designed and tested, demonstrating that fibres from tyres can be used for industrial applications.

A theory is presented which describes the mechanisms involved in concrete pressures on formwork in wide sections. The main value of the theory is in providing a framework for analysing site data and indicating areas in which potential economies in design might be made. The horizontal pressure of concrete on formwork comprises two components whose magnitude depends -on the proportion of the vertical load taken by the particle structure and the pore water pressure. In normal formwork, the pore water pressure provides the major contribution to the maximum horizontal pressure and therefore any factor which increases the rate of load transfer from the pore water pressure onto the particle structure, will decrease the maximum pressure. For example, porous formwork will give lower horizontal pressures than impermeable formwork and the re-analysis of existing site data supports this prediction. Normal internal vibration does not have such a significant' affect on the maximum horizontal pressure as previously reported, but it can fluidify concrete to the depth of poker immersion. The elements of the theory are supported by an experimental programme, re-analysis of existing site data and new site measurements. These site measurements have shown that during underwater concreting a rapidly falling tide can cause the horizontal pressure to exceed the vertical pressure.

The use of high strength concrete in the construction industry has become more frequent as both the knowledge of the behaviour of the material and the confidence in its production have increased. An appropriate formulation of materials and mix proportions can result in significantly enhanced performance such as high early strength, reduced heat of hydration and increased durability. As a step towards obtaining optimum performance, an investigation has been carried out on the fresh properties (workability), temperature rise during hydration and strength development. This research was aimed at understanding the role of supplementary cementing materials in binary (OPC+PFA, GGBS, CSF) and ternary (OPC+ CSF/PFA, CSF/GGBS) combinations in these three areas. With respect to workability the use of binary mixes of PFA or CSF reduce the superplasticiser dosage required to obtain a target slump, whereas GGBS increases it. Optimum replacement levels of 10% CSF, 40%PFA+l0%CSF and 60%GGBS+l0% CSF were found at a water/binder ratio of 0.26. Binary mixes of 40% PFA or 60% GGBS reduce the peak semi-adiabatic temperature rise compared to their equivalent OPC mix at 0.26 water/binder ratio. Ternary combinations of 10% CSF with PFA or GGBS have shown significant reductions in peak temperature rise compared to their equivalent binary mixes. Measurement of the in-situ strength by temperature matched curing (TMC) has shown higher early age strengths but lower long term strengths for both binary and ternary mixes compared to cubes cured under standard conditions (20°C). Microstructural evaluation of hardened cement paste indicates that these differences in strength are likely to be associated with stresses generated at the paste/aggregate interface. A novel non-destructive technique to assess the in-situ strength has shown good correlation between conductivity and strength development of high strength concrete.

No description available.

No description available.

No description available.

The concrete delivery and pumping process is a stochastic system. If analysed deterministically there is the danger that the negative effects of the random distribution of events are not taken into account, leading to poor estimates of production and cost. By representing the system as a random process the construction engineer can firstly achieve improved estimates of the overall productivity and thus schedule deliveries better, and secondly, determine the effect of non-anticipated events such as excessive delivery or pour times. The outcome of this research is a better understanding of how cyclic construction processes are managed and planned at a grass roots level. Firstly, by applying lean construction theories to concrete operations in the UK it was found that many are being carried out with an unacceptable amount of wasteful activities. By understanding lean construction principles some headway can be made to ensure that in future this waste is not only understood but also eliminated. Secondly, a multiple regression analysis was carried out with excellent results. Not only was it possible to identify those factors that most effect the performance of concrete placing, but also a model was developed that allows planners and engineers alike to accurately predict key responses such as pour duration and expected productivity. Finally, a simulation analysis was carried out which highlighted how the overall process reacted to changes in key times such as pump, interarrival and waiting time on site. By knowing how the process behaves and reacts to change it is possible to calculate the optimum operating conditions.

In recent years great advances have taken place in the use of masonry in building construction. Where as the number of storeys has increased substantially, the thickness of the wall has decreased. An important factor in the development of masonry structures was the introduction of the concrete block in the early 1900's. This added a new dimension to the construction and design of masonry structures. Greater flexibility was provided by the use of hollow filled and solid blocks utilising different colours, shapes and texture for interior and exterior masonry elements. The use of hollow blocks provided the advantages of using reinforced concrete filled masonry elements without the need for formwork. Reinforced blockwork masonry consists of four component materials, namely the concrete block, mortar, concrete infill and reinforcement. These four materials give masonry non-homogeneous properties compared to those of concrete. Differences in the mechanical properties of the four materials, the wide variety of block units available of different shapes and geometry, and the direction in which the masonry element is loaded all have an affect on the capacity and behaviour of the masonry structure. This present investigation consists of experimental and theoretical studies of the effects of the non-homogeneity of masonry, and of using different concrete infill and mortar types on the compressive strength and behaviour of blockwork masonry prisms compressed axially in two directions, normal and parallel to the bed face. Methods are suggested to determine the ultimate compressive strength of blockwork masonry, f'm. Finally the study investigates the effect of using different percentages of lateral and vertical reinforcement on the capacity and behaviour of reinforced concrete blockwork columns. A new method of predicting the capacity of reinforced concrete blockwork masonry columns subjected to axial compression is proposed.

The use of calcium sulfoaluminate (CSA) cement as a concrete material can save energy by 25% .and reduce CO2 emissions by 40%. The potential of using ggbs, pfa, bottom ash, pyrite ash and other by-product and waste materials to produce the CSA cement can result in further environmental benefits. The research undertaken in this investigation aimed to explore the potential of CSA cement as the main binding material for structural grade concrete, identify the limitation of this material in this context and suggest possible applications for the resulting concrete. The experimental study covered a number of variables, anhydrite content, OPC and lime Inclusion, water/cement ratio and curing regimes. The investigation encompassed the preparation of CSA cement in the laboratory and the use of a commercially produced CSA. The systems investigated included paste specimens prepared with laboratory produced CSA and commercially manufactured CSA and concrete specimens prepared with the commercially manufactured CSA cement. The investigation in paste included hydration product identification using X-ray diffractometry and scanning electron microscopy, expansion and compressive strength development. Setting time of CSA cement paste was determined using samples made with the commercially manufactured CSA cement. The properties of fresh and hardened concrete investigated were setting time, workability using both slump test and Tattersall's two-point test, expansion, compressive strength, indirect tensile strength, flexural strength, oxygen permeability, water absorption and rapid chloride permeability. The research carried out in this investigation on CSA cement paste established that ettringite was the main product of hydration. The hydration reaction occurred at a fast rate, with hydration being almost complete within a week after casting. Formation of ettringite as a result of CSA and anhydrite hydration did not cause expansion but in the presence of calcium hydroxide in the system, resulted in expansion. In systems where expansion was evident after long-term water storage, it is suggested that this had resulted from the ettringite imbibing water and expanding. This expansion was found to be controlled by the presence of internal constraints, such as unhydrous particles or aggregates (in the case of concrete). The use of low water/cement ratio and the resulting low water absorption can further reduce such expansion. Concrete workability was improved in CSA cement and anhydrite systems over that of control OPC concrete resulting in lower water demand. The use of OPC as cement replacement in CSA concrete adversely affected the workability and accelerated the initial setting time. The compressive and flexural strength of concrete made with CSA cement and anhydrite were considerably superior to those of control OPC concrete but, in general, were comparable with respect to their indirect tensile strengths. However, compressive strength was found to degrade by 10-20% with prolonged water storage and the OPC, as cement replacement, did not contribute significantly to strength. The need for water for CSA cement hydration was generally higher than the mixing water required for workability. As a consequence, CSA concrete is expected to have lower capillary porosity than OPC concrete. This fact was manifested in the lower water absorption value found for CSA concrete. High oxygen permeability found for CSA and the inconclusive results of the rapid chloride permeability test suggest that further research into the durability performance and durability related properties is required. The high early-age flexural strength of CSA concrete is an advantage in rigid pavements and pre-stressed concrete. The low pH of CSA concrete is another advantaged when glass or vegetal fibres are used. The concrete, however, needs to be of low permeability to safeguard against steel corrosion.