Shirasu is a kind of volcanic ashes, and is widely distributed in South Kyushu. It has a little lower melting and frothing temperature in comparison with other materials of artifical lightweight aggregate, and in homogeneous nature it can be mined at once abundantly and easily. The author has hit upon on idea that he will be able on that account to get a low-priced artificial lightweight aggregate made from Shirasu, and has manufactured for trial artificial lightweight sand and gravels (a tentative name; Calderite). Then, the author made an experiment on the basic data of the properties for aggregate, statical properties and elastic properties, and ascertained its practicability. Calderite sand belongs to 2 sort, C class on classification of JIS A 5002. But, Calderite sand seems to come a little short of the requisite strength of aggregate for fine aggregate of structural concrete, so it is necessary to make further studies of the formula of manufacturing. Calderite gravel belongs to 2 sort, C class or 3 sort, C class on classification of JIS A 5002. The author has proved that Calderite aggregate concrete can adequately be put to use, upon comparison with every standard from the results of the experiment on statical properties and elastic properties of Calderite aggregate concrete. But, Calderite manufactured for trial in generally felt a little soft and brittle. Then, it is necessary to study further as to the temperature in kiln and formula of manufacturing etc., and if so, it is hoped that the improvement of its quality will be made accordingly.
It is the aim of this paper to present the results of fundamental investigation of the mechanical properties of lightweight aggregate concrete for structural use. Four domestic lightweight aggregates and one normal weight sand-and-gravel aggregate have been prepared for the investigation. The data have been reported on the properties of stress-strain diagram under uniaxial loading, the static and dynamic moduli of elasticity, Poisson's ratio, the relationship between compressive and splitting strengthes, and the failure criterion for concrete under combined stresses produced by axial and torsional loading of cylindrical specimen. Consequently, the following main results have been obtained by comparing various concretes on the bases of equal compressive strength. (1) The test values of moduli of elasticity (Initial tangent modulus; Ei, Secant modulus at the stress of 0.3 times of compressive strength; E0.3F, and Dynamic modulus of elasticity; Ed) of lightweight concrete are somewhat lower than the normal weight concrete, and the rate of decrease of these values generally depend on the unit weight of concrete. (2) The values of Poisson's ratio under the usual range of structural stresses are about 1/5-1/6 regardless of kind of concrete. (3) The ratio of the compressive strength to the splitting strength of lightweight concrete is slightly larger than in normal weight concrete. (4) The failure criterion for lightweight concrete analized according to Mohr's theory of failure differs from that in normal weight concrete. However, the failure criterion by octahedral stress analysis is somewhat independent of the kind of concrete.
Qualities of lightweight aggregate such as its specific gravity, shape of particles and grading can be controled in its producing process, and these factors will have important effect on the quality of structural lightweight concrete. To find sufficient quality of the aggregate to be used in structural lightweight concrete, the relation between these factors and compressive strength of concrete were investigated. Four types of coarse aggregates were used; the coated-type expanded shale, the peletized-type expanded shale, and the river gravel and crushed stone. River sand was used in all concrete mixes. The particles of expanded shales were previously divided into 7 groups of specific gravity ranging from 0.9 to 1.6, and a certain class from them in which all particles had almost uniform specific gravity was used in a concrete mix. The concrete mix was determined by trial mixes so as to obtain the highest possible volume fraction of coarse aggregate using 1:1 mortar (W/C=30%). The compressive tests were carried out on φ10×20cm cylinders, and the main results obtained are as follows. (1) The relation between the specific gravity of expanded shale aggregate and the compressive strength of concrete appeared differently in accordance with the strength level of concrete. In the case of high strength concrete, the strength was limited by inherent strength of aggregate, and its inherent strength of aggregate was proportional to the specific gravity of the aggregate. (2) If we evaluate the desirable quality of lightweight concrete in the form of specific strength, the ratio of strength to the specific gravity, there is the most suitable specific gravity of the aggregate which brings the maximum specific strength of concrete. From the results of this experiment, the most suitable value of specific gravity was estimated as follows for each strength-levels of concrete: The required concrete strength (kg/cm2) Suitable s.g. (Saturated Surface-dry) 200∼300 1.3 about 400 1.4 about 550 1.5 about 700 1.5∼1.6 (3) The shape of the particles does not make any difference to the specific strength of the concrete, whereas the grading is one of the factors that affect the strength of concrete.
Recently, high strength artificial lightweight aggregates are being used for lightweight concrete as structural material in this country. Lightweight concrete seems to have different property from that of normal concrete, and requires specific treatment in the design and execution of structures. In order to study the fundamental properties of the lightweight concrete with artificial lightweight aggregates, measurement and observation were made of the consistency of fresh lightweight concrete and of the compressive strength and static modulus of elasticity of hardened lightweight concrete. The results obtained from these experiments were discussed in comparison with those of normal concrete. The diagonal tension test and the fatigue test were conducted on the beams of lightweight concrete and those of normal concrete. The investigation was made of their properties of the diagonal tensile strength, the fatigue properties, the behavior of the bond stress distribution, the behavior of the crack, and so on.
The object of this study is to examine the strength and deformation characteristics of reinforced concrete slabs made of structural lightweight aggregate (Lionite sand and gravel-pelletized type), in order to ascertain the adequate safety of the composite slab structures to which the material is applied. Twelve slab specimens having 3/5 scale to standard design dimensions, and sixteen beam specimens were tested under static load to failure with various support and loading conditions. Normal concrete specimens were also tested for the purpose of comparing the characteristics of lightweight ones. This limited investigation indicates that the Lionite concrete has almost the same strength properties as normal one and may be used with sufficient safety. As to the deformation, lionite concrete specimens showed a little larger deflection than normal concrete. However, the discrepancy of their deflection was much smaller than that of modulus of elasticity. Two-span continuous slab specimens were considered to have failed in punching shear, though the corresponding simple slab specimens were in bending moment. This indicates that the carrying capacity of slab structures should be examined for punching shear rather than for bending moment when the degree of restrainment becomes higher.
This report includes the experimental study of following problems. (1) When the density of coarse aggregate is low, artificial lightweight aggregate concrete is easy to segregate during its consolidation or transportation. (2) As the result of (1), more defects or cold joints are apt to form than in the case of ordinary aggregate concrete. (3) There is a tendency that big air bubbles remain on the concrete surface, and when the frame boards are removed they carry off part of the concrete with them leaving its surface in rough appearance. With respect to (1), the degree of segregation of coarse aggregate under various mixing conditions was investigated by letting concrete run down a short oblique chute. Concerning (2) and (3), the cause of these phenomena was pursued from both mixing and consolidating conditions, and the method to prevent them was found to some degree.