Practice Periodical on Structural Design and Construction

Researchers and designers starting investigations and work involving high-strength concrete, may face difficulties in producing high-performance concrete, including mix design and other practical issues. This question is still vital and significant in many countries in the world where the high-strength concrete industry is still developing. The hurdle of poor approaches (available in the literature) tackling this issue has encountered the authors of this paper when a major project on performance of high-strength concrete columns in fire was started at the University of Ulster. This paper is constructed in an easy way to simplify the method of producing high-strength concrete. The present paper includes the results of 15 trial mixes, where issues such as using silica fume and superplasticizer are discussed. This paper addresses new-to-the-field researchers and designers (worldwide) beginning studies and work involving high-strength concrete.

This investigation was conducted to collect state-of-the-art information on the strength and durability of roller-compacted concrete (RCC) for pavement construction made with and without supplementary cementitious materials, and to describe the construction experience gained in two pavement projects (Projects I and II) recently completed in Wisconsin. Project I deals with performance of conventional high-volume fly ash (HVFA) concrete pavement having a roller-compacted, no-fines permeable base course containing fly ash obtained from an SO₂ control technology (dry desulphuring process), and Project II deals with RCC pavement (RCCP) containing 30% ASTM Class C fly ash. Past studies have shown that mechanical behavior of RCCP is similar to that of conventional paving concrete. However, nonair-entrained RCC is susceptible to freezing and thawing (F and T) damage if critically saturated when subjected to freezing actions. Laboratory testing of specimens derived from the pavements showed excellent results for conventional HVFA pavement, and satisfactory performance of the RCCP except for F and T resistance. Specimens from the RCCP performed poorly in laboratory freezing and thawing testing according to ASTM C 666, Procedure A. However, they showed adequate performance for up to 210 cycles of F and T when tested in accordance with ASTM C 666, Procedure B.

In the process of manufacturing manhole inlets, strengthening rebars are placed at each side around the holes that are precast through formwork. Manufacturers have found it more economical by first casting the inlets and then forming the holes by coring. To give more flexibility to a later coring, in terms of location and size of the holes, manufacturers requested to eliminate the strengthening rebars. This raises a concern as to the structural performance of the cored inlets. For this reason, 15 tests were conducted on six specimens of manhole inlets to evaluate and compare the structural performance of specimens with cast holes versus cored holes. It was concluded that the specimens with cast holes performed better than those with cored holes in both serviceability and ultimate load capacity. The coring construction without strengthening rebars is not acceptable. Recommendations were made for both cored-hole and cast-hole constructions.

Simple methods for determining the corner crushing strength and the in-plane stiffness of masonry infills are developed. The methods are applicable to structural clay tile, clay brick, and concrete masonry infills and to both steel and concrete bounding frames. The corner crushing strength is determined as a function of the infill thickness and the infill prism compressive strength. The stiffness is determined using a stepwise function of the displacement and is a function of the relative stiffness of the infill to the frame. The only infill material property required for the stiffness is the modulus of elasticity. The methods were developed by looking at a wide variety of tests as reported in the literature.