This thesis comprises of two different kinds of work. The first part is focussed on existing experimental data. Investigations and observations of the behaviour of plain concrete under triaxial and multiaxial compression following cyclic loading and a variety of stress paths has been presented. The behaviour of concrete with different constituents was also investigated. The directions of the plastic strain vectors were identified. Two loading surface were also identified: (i) the Peak Nominal Stress surface (PNS) which was identified from the peak stresses recorded from stress control tests and (ii) the Volume Transition Stress surface (VTS) which determines the onset of the volumetric dilation. The plastic VTS is the surface which was identified from plastic strain components only. At this surface, the directions of the plastic strain vectors are purely deviatoric. A proposal for the shapes of the yield surface for concrete is given. These shapes were identified by the plastic work contours and also from the directions of the plastic strain vectors assuming the associated flow rule. This assumption has been verified by examining the normality of the plastic strain vectors to the PNS surface. Following the investigation of the experimental data, an examination of various advanced plasticity models for concrete revealed the need to develop a new constitutive model with a suitable shape of the loading surfaces and with a better prediction for the stress-strain response. A new constitutive model for plain concrete has been developed using the previous work in this field at the University of Sheffield. The new yield surface was developed as a combination of a reflection of part of the peak nominal stress surface (PNS) and a quartic function. The continuity, the convexity and the normality of the yield surfaces were ensured. The model was calibrated and the optimum values of the thirteen material constants are presented. This is followed by a sensitivity study with simulations of a wide range of existing experimental data. Simulations of concrete with different constituents are also presented. The formulation of the model was simplified and verified by using numerical derivatives. A comparative study between the analytical and numerical derivatives of the constitutive model is presented. The sensitivity study and the simulations of experimental tests showed that the new constitutive model is: (i) easy to calibrate using only data from uniaxial compression tests and one triaxial compression test, and (ii) gives very good predictions of stressstrain response of different types of concrete under triaxial compression stresses and at different levels of confinement all the way to the peak stress state.

Significant reduction in both strength and durability of concrete is brought about by voids left within the concrete once it has hardened. These voids can arise from a number of sources both intentional, in the case of air-entrained voids introduced by admixtures batched to provide a structure that can withstand frost attack and unintentional in the case of entrapped voids that arise due to characteristic of the sand and aggregates, excess water added and a lack of consolidation whilst plastic. Aggregate form, shape and texture are known to influence the way particles pack together and therefore the amount of space left between and amongst the particles. The second phase of this study has used desktop flat-bed scanning to record aggregate profiles, both raw particles and aggregate shape profiles taken from the curved surface of core samples, to classify the shape and then provide a protocol for defining the shape. This study has shown the photographs provided originally in Concrete Society Technical Report 11 and now recently re-introduced into the UK Annex of BS EN 12504-1:2009 Testing concrete in structures – Core specimens – Taking, examining and testing in compression, provide a misrepresentation of the curved surface of the core. A curved surface cannot be recorded faithfully by a 2D camera image. An accurate representation of the curved surface of concrete core samples has been obtained by the use of conventional desktop scanners, albeit using relatively high image resolution. By a novel yet simple modification, concrete core samples have been mechanically rolled above a modified flatbed desktop scanner driven by the crosshead so as to align directly above the cold cathode fluorescent (CCF) light source and the scanning charged coupled cross-head image recording device. A method of assessing the amount of voidage found within the curved surface of concrete core samples has been developed. A freely distributed software programme was used to process all images to determine percentage voidage and voids size distribution among other attributes. A second freely available statistics software package has been used to analyse the results. iii The second phase of the study has used the same scanning technique to classify 2D aggregate profile as used for voidage shape recognition taken from the curved surface of core samples. Three simple shape factors have been used, one developed specifically for this study. By means of Riley Circularity, Percentage Concavity and Aspect Ratio core surface aggregate profiles, raw aggregate shapes and voidage found on core samples have been classified. The objective being to determine if the aggregate within a sampled concrete has changed from that intended, possibly due to crushing oversize material or just changes within the source that would provide a means of assessing any influence aggregate shape change may have had on entrapped voidage and the effect that has had on the strength of the concrete. Scanner performance and calibration has been checked using high resolution calibration sheets. The image resolution was found to be accurate to 2.5% at 0.5mm diameter when scanned at 1200 dpi. This enabling the threshold to be investigated between entrained and entrapped air voids so as to allow discrimination between any combinations of the two found on a core sample. The equipment, equipment modifications, procedures, test protocols as well as the imaging software and statistical analyses packages included in this study have been chosen so as to allow others to utilise the benefits such analyses offers. The recent acceptance and drive to recycle materials for use as construction aggregate can benefit from classification by these procedures that until now have not been included in any published Standards. The procedures developed during this study have been published in the Magazine of Concrete Research, Dec 2010 and presentations given by invitation to joint meetings of the Concrete Society/Institute of Concrete Technology at Loughborough and in London, 2011.

No description available.

The overall solid packing see mix design method of Brouwers and Radix was modified by developing an optimisation tool, facilitating the proportioning normal weight SCCs (NWSCCs) and L WSCCs. The method comprised two concepts: filling the voids within the loosely packed aggregate fraction with appropriate paste and comparing the overall particle size distribution (PSD) of solids in the mix with the model PSD. To implement this method, the influence of supplementary cementitious materials (SCMs), fillers and chemical admixtures on the paste properties was investigated; moreover, physical properties and packing of normal and lightweight aggregates (L W As) were studied. The influence of two L WAs, three superplasticisers and three SCMs/fillers on the fresh properties and compressive strength of LWSCCs was evaluated, followed by a detailed study on L WAs and SCMs/fillers effect on engineering and durability properties of L WSCCs. The proposed mix design modification yielded highly flowable, strong and durable L WSCCs for structural precast applications. Successful LWSCCs required carefully optimised paste composition and paste/aggregate content. L W As water absorption characteristics and cement-superplasticiser compatibility strongly influenced workability and workability retention of LWSCCs. The effect of aggregate composition and aggregate/paste content on fresh, hardened and durability properties of structural NWSCCs was studied. The proposed mix design allowed manufacturing NWSCCs with moderate workability, high strength and paste content lower than typically reported. Most of NWSCCs properties correlated with the average spacing between the aggregate particles, allowing for engineering of NWSCC properties by its adjustment.

No description available.

This thesis reports experimental work, carried out as a PhD study, investigating the possible re-use of glassy secondary materials as aggregate in concrete. A study of the relevant literature suggested that slag from the Imperial Smelting Furnace method of zinc production (ISF slag) and Cathode Ray Tube (CRT) glass from end of life computer monitors and television screens would be promising materials to test. The main issues identified as being of most concern relating to the use of these materials were the potential for alkali-silica reaction (ASR) due to the glassy nature of the aggregate materials, in-service leaching of heavy metal ions, namely lead, zinc and barium from the aggregates and the possibility of a delay in set caused by the addition of these materials to concrete or mortar mixes. A comprehensive study has been completed that has included characterisation of the secondary aggregate materials, their incorporation into concrete mixes and their effect on ASR, leaching and retardation of concrete set. Methods have been identified to minimise these potential problems where they have been shown to be an issue. These include the recommendation of various additions, depending upon the specific problem being overcome, ranging from cement replacement materials, such as pulverised fuel ash (PFA) and ground, granulated blastfurnace slag (GGBS) to chemical additions such as barium and calcium chlorides. Overall, it has been shown that the ISF slag and CRT glass could prove to be useful secondary materials for use in the construction industry and it is hoped that their specification and use will be forthcoming as a result of this study.

Lytag is a synthetic lightweight aggregate which has been in commercial production for many years. Its production process involves sintering pulverised fuel ash at approximately 1200-1300°C to produce spherical, chemically inert pellets with a porous structure, which is graded into coarse, medium and fine grades. Concrete, produced with Lytag coarse and fine material, has been extensively studied to assess its basic material and structural properties. Few data, however, are available on concrete made with Lytag coarse material and natural sand fines. The aims of this investigation were basically two-fold. Firstly the material properties of Lytag-sand concrete were investigated and an extensive study of various properties such as strength, moduli of elasticity, Poisson's ratio, stress-strain characteristics, shrinkage, moisture movement and creep are reported. Secondly, the structural behaviour of reinforced Lytag-sand concrete T-beams failing in shear and flexure was also investigated. As with all concretes, these properties are affected by the constituents which make up the concrete, in particular the aggregate. With this in mind microscopic examination of several Lytag pellets was carried out using a scanning electron microscope (S. E. M. ) in order to observe some of the physical characteristics of Lytag aggregates in general. An attempt was then made to relate these characteristics to the water absorption of Lytag aggregates. The test results show that concrete strengths of 60 N/mm2 are easily obtainable using Lytag and sand, and that in general a lower cement content is required for Lytag-sand, than for other sand replaced lightweight concretes, in order to achieve a given compressive strength. Shrinkage and creep are comparable with the range of values obtained for concretes made with various dense aggregates but when compared to concretes made with good quality dense aggregates values of the order of 1.5 times the dense concrete values are to be expected.

No description available.

No description available.

Silicafume (SF) has been used as a partial replacement for cement in concrete and experiments have been carried out to measure the durability of the mixes. The SF mixes were made with 20% SF replacement of cement and waterlcement (wlc) ratios of 0.3 and 0.46. Three different curing conditions were used to simulate different site conditions and tests were carried out at 3,28 and 90 days after casting. The following properties were measuredfor the two SF mixes and the two control (OPC) mixes for each of the ages and curing conditions: corrosion rate of embedded steel by linear polarisation, electrical resistivity, carbonation depth, water vapour permeability, chloride permeability, oxygen permeability and porosity from helium and mercury intrusion. Samples were also investigated by thermogravimetric analysis. The resulting data matrix was analysed by using the method of analysis of variance to quantify the effect of the SF on the properties tested and their sensitivity to age and curing. It was also analysed by multiple regression to identify major effects of one property on another. It was concluded that SF will reduce the corrosion rate and that the major contributing factor is the substantial increase in resistivity that the SF causes. This increase in resistivity was found to be highly sensitive to cold curing in the short term but this effect was not permanent. The cause of the increase in resistivity is believed to be the depletion of calcium hydroxide which is caused by the pozzolanic activity of the SF. The analysis also indicated that the SF reduces the porosity in the .01-.15)1m size range and that this has a major influence on the durability.