Journal of Materials in Civil Engineering

In construction of a man‐made island using a cofferdam and fill, problems are often encountered, such as sliding failures of a soft seabed or ruptures of the cofferdam. A new filling method, underwater placement of a light and self‐hardening slurry, presents great advantages that are confirmed by theoretical analysis. An appropriate slurry for this new method, containing fly ash, volcanic ash, and a small amount of cement, is developed from experimental investigations. This light, self‐hardening slurry greatly reduces the earth pressure and increases the safety factor of the island, and it also makes subsequent construction work easier. Strength development of the slurry is inhibited by low temperature, but this can be compensated for by a small increase in the cement content. Practical slurry compositions are also proposed based on laboratory studies, which included test‐tank tests. It is concluded that underwater placement of fly‐ash slurry is a viable method for man‐made island construction.

In the Hakucho Ohashi (Muroran Bay Bridge) project, a man‐made island of 67 m diameter has been made by underwater placement of a self‐hardening slurry on a soft seabed. From October 1988, $53\text{,}600m^3$ of slurry, containing 46.1 Gg of fly ash, 22.2 Gg of volcanic ash, and 2.6 Gg of cement, was filled into a steel‐pile cofferdam during a three‐month period. During this filling work, great advantages of the new method over conventional methods were confirmed: (1) Reduced lateral earth pressure on the cofferdam walls and the resulting smaller bending moment and lateral displacements; and (2) higher strength of the island for subsequent construction work. In spite of low temperatures in winter, heat supplied from the slurry kept the fill temperature above 10 °C, so strength development was higher than expected. From these results, we can conclude that the underwater placing method is a great advance in man‐made island construction and contributes to the creative use of waste fly ash.

Natural pozzolans (NP) have been introduced as partial cement replacement to minimize some durability problems encountered with ordinary portland cement (OPC) use in the Arabian Gulf. However, NP addition affects concrete drying shrinkage and leads to a slower strength development, which makes a longer curing time necessary. This research compares the strength and drying shrinkage of NP mortar cured under hot‐weather Gulf conditions and under normal conditions. The effect of various NP replacements was also evaluated in this study. Under hot weather, results showed that OPC mortar generally maintained higher strength than NP mortars. Also, under hot weather, mortar strength increased in early ages at a higher rate than that of normally cured mortars. However, the strength of these hot‐weather samples declined at later ages, while normally cured ones maintained their strength increase. Shrinkage results showed that normally cured NP samples have lower shrinkage values than those of OPC. However hot‐weather NP samples showed early higher shrinkage values than OPC; but later, at one year of age, all samples showed approximately equal values. Moreover, shrinkage of hot‐weather NP samples decreased as their initial normal curing periods increased.

Expressions for the protected‐paste volume of air‐entrained cement paste are derived using the hydraulic‐pressure mechanism of frost damage. The protected‐paste volume is the total common volume of cement paste protected from frost damage by all the air voids in the paste. The derived expressions are shown to reduce to known results for simple geometrical arrangements of air voids. The relative importance of air‐void parameters, material properties, and environmental parameters are deduced from the structure of the derived expressions. It is shown that material and environmental factors have at least as great an effect as air‐void parameters on the protected‐paste ratio. Though the expressions have been derived on the basis of the hydraulic‐pressure mechanism, it is suggested that the concept of protected‐paste volume as well as the form of the expressions may be applicable to other mechanisms of frost damage.

TO investigate the overall thermal conductivity characteristics for composites of two dry porous materials, an experiment was conducted to measure the thermal conductivities for mixtures of fine sand and white lime, fine sand and coal powder, and salt and sawdust at various volumetric mixing fractions using a transient line‐heat‐source device. Results indicated that the low‐thermal‐conductivity material has a pronounced influence on the heat‐conduction process in the composite and the overall thermal conductivity does not obey a simple mixing law. The concept of basic heat‐transfer routes was introduced to physically describe the heat‐transfer mechanism. A probability‐based group‐contribution theory was used to obtain an empirically adjusted theoretical equation. This equation fit measured data with an $R^2$ of 0.96 or better, with a significance level of 0.001. The general effective media (GEM) equation based on the effective media and percolation theories was also used to describe the experimental data.

The effect of service‐load‐induced internal damage in advanced filamentary composite materials has for some time been a topic of extensive research. It is well known that the stiffness of the material system is degraded as load is applied and damage accumulates. A computational simulation of the processes by which the internal damage propagates was developed for studying the effect of the complex interactions among identified internal damage mechanisms. The approach considers the random distribution of initial matrix flaws (microcracks and micropores) and weak fiber‐matrix interfacial bonding, the random strength properties of the fibers, and load transfer in the vicinity of broken fibers through matrix shear, and it employs an iterative, time‐stepping technique to simulate damage propagation under increasing load and over periods of sustained constant load. The developed model is employed to simulate the response of strands of Kevlar 49/epoxy to specified loading conditions. The statistical nature of the effect of preloading on the stiffness and strength degradation of continuously loaded strands is demonstrated and discussed.

In this study, the effect of replacing calcined gypsum in wallboards with fly ash was studied. Three types of fly ash produced in Alberta, Canada, were used for replacement of as much as 40% of the calcined gypsum in wallboards. All the three types of fly ash were pozzolanic as well as self‐cementitious. Wallboard specimens were prepared in the laboratory, placing gypsum, fly ash, pulp, starch, and foam slurry between two sheets of paper. Strength and other physical properties of wallboards, with and without fly ash, were determined. It was concluded that as much as 30% gypsum in the core of wallboards can be replaced by fly ash with very little detrimental effect on the properties of the wallboard. The results indicated there was only a slight loss in the compressive strength for 30% replacement of gypsum with fly ash. Wallboards containing fly ash developed high core hardness, nailhead pull resistance, and water resistance. They were also observed to have lower thermal conductivity than those containing only calcined gypsum.