Aggregates for Bituminous Materials Aggregates make up the bulk of bituminous materials; the percentage by weight ranges from about 92% for a surface course asphalt to about 96% for a dense, heavy-duty and high-modulus base asphalt concrete. The aggregate has important effects on the strength and stiffness of bituminous mixtures. In asphalt concrete mixtures, the […]
Mix design is the process of selecting the proportions of cement, water, fine and coarse aggregates and, if they are to be used, additions and admixtures to produce an economical concrete mix with the required fresh and hardened properties. It is often, perhaps justifiably, referred to as ‘mix proportioning’ rather than ‘mix design’. The cement
There are a wide variety of methods and techniques available for the non-destructive testing of structural concrete, which can be broadly divided into those that assess the concrete itself, and those which are concerned with locating and determining the condition of the steel embedded in it. We are going to describe three well-established tests for
Durability can be defined as the ability of a material to remain serviceable for at least the required lifetime of the structure of which it forms a part. Standards and specifications increasingly include requirements for a design life, which can typically be 50 or 100 years, but for many structures this is not well defined,
Degradation of Concrete The degradation agencies that affect concrete can be divided into two broad groups: those whose action is initially chemical, before subsequently leading to loss of physical integrity; these include sulphates, seawater, acids and alkali– silica reactions those which directly lead to physical effects, such as freeze–thaw and fire. We will now consider
Durability of Steel in Concrete Nearly all structural concrete contains steel, either in the form of reinforcement to compensate primarily for the low tensile and shear strength of the concrete, or as prestressing tendons that induce stresses in the concrete to oppose those due to the subsequent loading. Sound concrete provides an excellent protective medium
Constituents of Bituminous Materials Bituminous materials consist of a graded aggregate bound together with bitumen. In addition, the mixture contains a small proportion of air. Thus bituminous materials are three-phase materials and their properties depend upon the properties of the individual phases as well as the mixture proportions. The two solid phases are quite different
In this aritcle, we will briefly discuss some alternatives to Portland cement. These include calcium aluminate cement, which has been in use for a hundred years or so, and some cements that have had more limited use or are currently being developed and are not yet in widespread use. This latter group is of particular
Hardened cement paste (HCP) formed from the hydration of mixtures of Portland cement, admixtures and additions has strength and other properties that could make it suitable for use as a construction material in its own right. However, it suffers from two main drawbacks – high dimensional changes, in particular low modulus, high creep and shrinkage,
Civil engineers are responsible for the production, transport, placing, compacting and curing of fresh concrete. Without adequate attention to all of these the potential hardened properties of the concrete, such as strength and durability, will not be achieved in the finished structural element. It is important to recognise that it is not sufficient simply to