This paper presents three examples of low density, all lightweight aggregate concrete applications. These applications represent "high performance" concrete because the concrete properties could no be achieved with the usual materials and methods. Each example used rotary kiln produced expanded clay lightweight aggregates to obtain concrete densities as low as 75 lb/ft3. Where required, relatively high strength concrete (6000 psi) was produced. In another instance, the compressive strength was purposely limited to less than 3000 psi. In each case the concrete met the needs of the user, resulting in significant cost savings.

A new mathematical model to study the problem of fiber pullout in fiber reinforced cementitious composites is briefly introduced. However, with an objective of optimizing fiber-matrix interfacial properties, the main focus of this paper is on the parametric studies carried out using the proposed model. Stresses required to cause initial, partial and complete depending of the fiber-matrix interface are analyzed based on shear lag theory, and closed-form solutions are derived to predict the complete pullout response. Influence of radial stresses (normal contact stress) acting at the interface is considered using the shrink-fit theory of elasticity. Analysis show that the interfacial frictional shear stress decreases with increase in Poisson's contraction of fiber. Furthermore, based on energy considerations, an analytical solution derived to compute interfacial coefficient of friction depicts that interfacial coefficient of friction decreases with increase in pullout distance. Increase in matrix wear resulting with fiber pullout is most likely responsible for the decay of coefficient of friction. Parametric studies are carried out to investigate the influence of fiber-matrix interfacial properties (adhesion bond shear strength, normal contact stress coefficient of friction) and elastic modulus of fiber. Results suggest that for a given set of interfacial properties, initial depending stress, maximum pullout stress, catastrophic debond length, interfacial shear stress distribution, and overall pullout response significantly depend upon fiber elastic modulus. Given the fiber elastic modulus, recommendations are made as to how efficiency of fiber in pullout could be improved by modifying the interfacial properties.

Concrete may be considered a three phase material, consisting of cement matrix, aggregate and the interfacial transition zone (ITZ). The ITZ is studied usually by collecting backscattered electron (BSE) images of polished samples of concrete and by carrying out a quantitative analysis of these images. This technique makes use of the contrast between pores and cement hydrates to analyse the microstructure. Once the images are collected, grey level thresholding is used to segment regions associated with capillary porosity. The size of the ITZ is determined using this data. Different techniques have been suggested to minimise errors introduced at this stage of the analysis. The authors have carried out an investigation on 17 different concrete mixtures in an attempt to assess the role of threshold values. The results indicated that the size of the transition zone is not affected by the range of threshold values used. However, the porosity of both the ITZ and the bulk cement paste varied with different threshold values. The paper proposes a method which can be used to determine a reliable threshold value.

Based on four strength parameters testing of three high-performance concrete (HPC) design mixes and parametric studies, the following conclusions have been made. Creep and shrinkage strains of HPC are lower than those in conventional concrete. Amount and type of coarse aggregates affect the value of modulus of elasticity. The modulus of elasticity of HPC should be determined through experiments with local materials. Beam sections that have large bottom flange are efficient for HPC application. The most significant property of HPC prestressed beam is compressive strength at release. Allowable compression at release has the most impact on span capacity, while allowable tension at service has minor impact. Prestress loss can be reasonably predicted by either the proposed method or AASHTO LRFD Lump Sum method. PCI deflection multipliers at final time are not accurate. The proposed multipliers which are the functions of creep coefficient can be used for conventional and HPC members.

This paper presents data on the performance of concrete containing ternary combinations of Portland cement, silica fume and fly ash. Porosity measurements show that the individual effects of silica fume and fly ash on pore size distribution are cumulative when both materials are added to Portland cement. Chloride diffusion and rapid chorine permeability test on concrete indicate significant improvements can be achieved through the use of these ternary combinations. There is a synergistic effect attributed to the early-age benefits of incorporating silica fume and the long-term improvements normally associated with fly ash. The final product is concrete with very low initial directivity values that continue to reduce with time. Simplistic service-life calculations indicate that high-performance concrete with ternary cementations blends may provide protection to steel reinforcement way beyond the normal expectations of engineers today. These results are not inconsistent with recent studies of marine exposed concretes, which indicate that the penetration of chlorides may eventually decrease to almost insignificant rates in concretes containing 30% to 50% fly ash.