The artificial lightweight aggregate has higher porosity and absorption than those of natural aggregate. It has been recognized that the higher water absorption property of artificial lightweight aggregate has a great deal to do with the mixing proportion of concrete and also with the properties of hardened concrete, such as drying shrinkage, durability and so on. In this study, the authors made some experiments relating to the effect of absorbed water of aggregate on the properties of artificial lightweight aggregate concrete. Three kinds of commercial lightweight aggregate, namely two kinds of expanded shale (coated type) and expanded clay (pelletized type) were used as coarse aggregate. In order to clarify the efficacy of absorbed water content, these aggregates were made to contain different amount of absorbed water by keeping them in water for different length of time. Fine aggregate was river sand in all the mixes. Fresh concrete was tested for consistency, and hardened concrete for compressive strength, tensile strength, flexural strength, Young's modulus, drying shrinkage and durability against freezing and thawing. The main results of the experiments are summerized as follows: (1) The consistency of fresh concrete is not affected by water absorbed in the aggregate. (2) The compressive strength of hardened concrete is little affected by absorbed water. (3) The flexural strength of concrete is little affected by absorbed water when it is cured in water, but when it is cured in air is remarkably deteriorated by the increase of water absorbed in it. (4) The shrinkage of concrete is smaller in an early stage of drying, when the aggregate containing absorbed water to a higher quantity is used instead of the aggregate in which water is absorbed for 24 hours. But in a later stage the shrinkage in question becomes larger than in the concrete in which the aggregate with water absorbed in it for 24 hours is used. (5) The durability of concrete against freezing and thawing depends very much on the quantity of the water absorbed in its aggregate. The durability becomes remarkably poor by using aggregate in which water is absorbed over 5∼6%.
It is the aim of this report to present the result of experiments in the effect of grading of two available artificial lightweight aggregates on the properties of mortar and concrete. The tests were divided into three classes. In experiment 1, specific character of aggregate at an interval of size and the effects of grading of lightweight sand were investigated. Consequently, we obtained a tendency that the larger the size of the aggregate, the smaller the specific gravity of the grain became and the larger water absorption grew. But the gradings of the sand which were composed of grains, gave a slight variety to the specific gravity, coefficient of water absorption and solid volume percentage of sand, even if the gradings were widely chosen. So the gradings had an inconsiderable effect on the properties of the mortar. In experiment 2, we investigated how the grading of fine sand, the grading of gravel and fine aggregate ratio affected the properties of concrete. As the result of the test, the aggregate ratio and the grading of sand had comparatively large effects on various kinds of strengths, but the grading of gravel affected only little. The quantity of surface water over the sand at the time of mixing had a large effect on the slump of fresh concrete, and the influence of grading was relatively small compared with it. In experiment 3, to study the fundamental effects of aggregates such as size, surface area, specific gravity and strength of aggregate on the properties of concrete, test was carried out using the cubic model aggregate made from paper vacancy, rubber, mortar and steel. In consequence, the characteristic of the aggregate including the grading had a great effect on compressive strength, tensile strength, static modulus of elasticity and specific gravity of concrete. It exceeded the effect of water cement ratio. As for the paper vacancy aggregate which was compared to lightweight aggregate, the effect of size on the properties of concrete became marked. Through the above mentioned three tests, it was indicated fundamentally that various kinds of strengths, specific gravity and static modulus of elasticity of concrete were affected by strength, specific gravity and the grading of lightweight aggregate. On the other hand, as for the artificial lightweight aggregate concrete actually used, the effect of grading on the properties of concrete was found to some extent but factors except grading such as the quantity of surface water over the sand effected it much more.
In Japan the pumping of concrete is generally in practice in the building projects to save labor because of manpower shortage in the country. But there are some problems in pumping the concrete, especially of the lightweight aggregate concrete. It is the aim of this report to present information on the above mentioned problems which has been obtained through the investigations into the practices adopted in several projects. The summaries are as follows: (1) The mix proportion of concrete is revised to some degree to make the pumping easier, although there has not yet been found a general standard. (2) In many cases, the water requirement in concrete mix is increased from 5 to 10kg per cubic meter of concrete and also is the fine/combined aggregate ratio increased from 3 to 5%. (3) The mix proportion of cement paste in concrete which is pumped up to comparatively high places (e. g. higher than 20m) has tendency to be increased. (4) By receiving high pressure during the pumping process, the lightweight aggregate absorbs much more water than when it is under atmospheric pressure, therefore, the workability of concrete becomes lower than what it was before the pumping. The decrease of slump is in many cases not more than 3cm but in some cases exceeds 10cm. (5) The entrained air increases or decreases, as the case may be, but the variation shows in many cases not more than 1%. (6) The compressive strength of concrete is also affected by pumping. In certain circumstances, there is decrease of strength, even at times at the rate of more than 10%. This phenomenon may be ascribed, though not thoroughly analyzed yet, to the water which has found its way into the lightweight aggregates during the process of the pumping, due to its pressure, and which oozes out into the bond between the aggregate and the cement paste and damages it, after the concrete is moulded. (7) Thorough irrigation of the aggregates in stock yard is effective in decreasing the amount of water to be pumped into the lightweight aggregates.
Recently, artificial lightweight aggregate has often been used in preparation of lightweight concrete for civil engineering structures, particularly as prestressed concrete structures. It is the objects of the present study to examine several behaviors of lightweight concrete girders, in respect of its elastic limit, flexural and shearing strength, and the results of the examination are discussed in comparison with the results of examination made of the behaviors of normal concrete girders. The specimens which are made from normal concrete and three kinds of artificial lightweight concrete, having 0.5 meters height of T-shape section and 8.4 meters length, which are specified in JIS A 5316, are tested under static load to failure with various loading conditions as follows. The flexural test has been carried out by the method according to JIS, having two central loads and 1.0 meter interval, the ages of specimens are 28 days. The shearing test has been carried out by two central objective loads and their situation has been decided according to the ratio of the shear span to the effective depth a/d, such as 2, 3, 4 and 6. The ages of the specimens are 122 to 156 days when the shear loading tests are practiced. The results obtained from these tests are discussed in comparison with those of normal concrete, and the main results are as follows; (1) The behavior of the flexural crack of the lightweight concrete girders is less than the normal one and its ratio is about 75 percents. (2) The girders with lightweight concrete has almost the same ultimate flexural strength properties as normal concrete girders and may be used with sufficient safety. (3) As to the shearing strength against cracking and breaking, the lightweight concrete girders show about 70 to 80 percent rate of normal concrete girders.
It is more than ten years since prestressed concrete (PC) was applied to the superstructure of concrete railway bridges in Japanese National Railways (JNR). Since then nearly 2000PC bridge girders have been constructed in JNR. To make the PC girder span longer, the Tokyo Construction Division hit upon an idea of using lightweight aggregate, and various researches and tests on concrete structure have been conducted since 1962, using artificial lightweight aggregate with burnt expanded shale. The live load of railway bridges is heavier than that of highway bridges. And the repeated stress by wheels of rolling stock have great effect on the fatigue strength of girders. Therefore, many kinds of basic tests have been conducted by placing stress on dynamic tests. When lightweight aggregate is used for prestressed concrete, its strength inevitably goes down. So, as the result of the tests conducted to research the tendency of decrease in the strength of lightweight concrete, it was decided to use natural aggregate together with lightweight aggregate. This has enabled us to obtain a compressive strength of 400 to 500kg/cm2 and a specific gravity lighter by 20 to 30per cent than ordinary concrete. A few points made known as the result of our researches and tests are: The Young's modulus of lightweight concrete is 40 to 60per-cent less than that of ordinary concrete. No special difference is seen in the bending strength, but there is a little decrease in the shearing strength. It is suggested, therefore, to make the allowable stress of diagonal tensile strength about 20per cent less than that for ordinary concrete. The elastic deflection at the time the girder is loaded is about twice as much as that in case of ordinary concrete, and its value is almost in inverse proportion to the Young's modulus. Based on the result of our researches and tests, the Kanayama Overbridge of the Tohoku Main Line, the elevated approach bridge to the Arakawa Bridge of the Sobu Main Line, etc. have been constructed since 1965, and investigations on these bridge girders are now being pursued.
The lightweight concrete for precast concrete curtain wall should have such properties as low slump, high density and early high strength, etc. This report describes (1) the results of the compressive strength tests of concrete with various mixes, (2) the comparison of properties between the synthetic lightweight aggregate concrete and the normal concrete regarding their compressive, tensile, and flexural strengths, permeability, absorption, drying shrinkage and durability, (3) the results of the vibration test on full size panels, and (4) some application examples of such curtain walls.
Recently lightweight concrete are increasingly used in making precast concrete units all over the world. This paper describes some plactical methods of applying precast lightweight aggregate concrete to the construction of building structures developed in America and Japan, and the advantages of making use of lightweight aggregate in this field are also discussed.
This report describes the compaction by internal vibrator for fresh concrete made with artificial lightweight aggregate. The pressure caused to the vibrator was measured at random in concrete by means of the pressure gage embeded in concrete. The acceleration was calculated upon the measured value of the pressure. Float of lightweight coarse aggregate occurred during the vibration within the range of about 20cm from the vibrator. This phenomena can be prevented by limiting the vibration at each point within ten seconds. The effective zone for compaction corresponding to four times as much acceleration of gravity is about 30cm from the vibrator.
This paper describes the preparation of vibrating compaction of concretes by the use of artificial lightweight aggregates, especially the consolidation on a vibrating table for dry mixes. The effects of vibrating frequency, amplitude, acceleration and time on the compressive strength of concrete were investigated. These test results are summarized as follows:- (1) The use of a vibrating table is a more effective method for obtaining consolidation of lightweight concrete in thin sections than internal vibration. (2) The frequency of 3000 to 5000vpm, the amplitude of 0.6 to 1.1mm and the acceleration of 5 to 10g concerning the vibrator table used for this study are found to be suitable for the compaction of lightweight concrete. (3) The length of time taken in vibration on the table can be somewhat shortened for lightweight concrete, although the optimum condition of compaction is dependent on the shape of the aggregate that was used. (4) When the internal vibrator of a rod type is used for lightweight concrete, vibration of higher frequency is preferred for efficiency. However, the distance between the pair of legs of the plug must be kept as close as possible.
To examine the durability of artificial lightweight aggregate concrete under the action of sulphates, two kinds of artificial lightweight aggregate (Lionite and Mesalite) and normal weight aggregate (River sand and gravel), three kinds of cement (normal portland cement, blast furnace slag cement-B and C) have been selected and used with some combinations. Concretes with the above-mentioned aggregates and cements, having water cement ratio of about 40% and 55%, at ages of one and four weeks' immersion in sulphate solution (Na2SO4 (20%)+MgSO4 (20%), mixed 1:1) were prepared and compared with the control concrete (in standard curing) having the same sorts of cements and aggregates. The degree of deterioration were measured in reduction of dynamic modulus of elastisity by flexible frequency (specimens: 10×10×40cm, by sonic apparatus), weight of specimens (10×10×40cm) and compressive strength (φ10×20cm) relative to control concrete respectively, over a period of one year. The test results show that artificial lightweight concrete have indicated the same good resistance and soundness to chemical attack of sulphate as normal concrete, and the damage of specimens made from lightweight concrete under action of sulphates is observed to be smaller than in normal concrete, even after one year's or 15 months immersion.
The present paper describes the results of the experimental and theoretical investigations made on the bearing capacity of lightweight aggregate concrete. Laboratory tests were conducted to clarify the effects of the dimension of the specimen, the ratio of footing area to loading area of the specimen and concrete mix proportion on the bearing capacity of the cylindrical concrete specimen, which was loaded to be subjected to circular pressure at the center of the top and supported by the entire surface at the bottom. The similar loading tests were also carried out on normal concrete. From this test, the following conclusions were obtained: (1) The bearing capacity (σu) was nearly proportional to compressive strength (σc) ranging from 200 to 400kg/cm2 for normal concrete, but σu was not proportional to σc for lightweight concrete. The ratio of the bearing capacity of lightweight concrete to that of normal concrete were about 1.0, 0.85 and 0.70 when the compressive strength was about 200, 300 and 400kg/cm2, respectively. (2) It is found, therefore, that the coefficients included in conventional empirical formulas to determine the bearing capacity of lightweight concrete should be varied in accordance with the change of concrete strength. (3) The results showed that there was no obvious difference due to the influencing factors, except concrete strength, between the normal and the lightweight aggregate concrete. Moreover, the characteristics of the approximate theoretical solution derived by the author were disccused and compared with the test results obtained and the solutions proposed by other researchers.
The remarkable differences are usually noticed between the stress-strain curves of lightweight aggregate concrete and the curves of river sand and gravel concrete in their gradient and the curvature of their curves. The shapes of stress-strain curves of various sorts of lightweight aggregate concrete were studied in detail by graphical analysis of curves showing their difference in stress-strain relations. And the characteristics of the finite difference curves obtained can be used commonly to classify the stress-strain curves for normal and lightweight aggregate concretes. The finite difference curves of stress-strain relations indicating cord modulus Δσ/Δδ on the ordinate and strain δ on the abscissa, were quite effective for distinguishing the characteristics of stress-strain curves, since they magnify the variation of the curvature of stress-strain curves. The graphical characteristics of finite difference curves may be summarized as follows. (1) The finite difference curves of stress-strain relations of concretes can be devided into three stages of comparatively linear parts, (1) early stage of slowly descending part, (2) steeply descending part and (3) last stage of slowly descending part. (2) Most finite difference curves consist of one or two stages. Typical patterns of finite difference curve are composed of (1)-(2) stages, (2) stage only or (2)-(3) stages of combination. These three typical patterns may also be corresponding to high strength type, medium strength type and low strength type of stress-strain relations, respectively. (3) The normal concrete and the lightweight aggregate concrete have similar combination patterns of three stages. The compressive strength of concrete corresponding to its above-mentioned patterns, however, varies with concrete composition (fine-coarse aggregate combinations). Since mechanical behaviors of concrete at a certain stress level are reflected in the characteristics of finite difference curve, the results of analysis of finite difference curves obtained in this report will offer a qualitative estimation of mechanical properties of concrete with various mix proportions and various aggregate properties.
It is the main purpose of this study to obtain information on bond strength of reinforcing bars for lightweight concrete as compared with that for normal river sand and gravel concrete. The influences of surface characteristic of reinforcing bars and methods of test were also investigated. Four types of bars were tested and three kinds of methods of test (pullout test, tension test and long prism test) were chosen. From the tests the following results were obtained and conclusions drawn: (1) The test date show no difference in bond strength between lightweight concrete and normal concrete, so far as both the kinds of concrete are equal in compressive strength. (2) There is correlation among the test results by three different test methods. (3) The pullout test gives the most reasonable measure to evaluate the relative effectiveness of reinforcing bars in respect of the anchorage bond. (4) The long prism test serves to evaluate the effectiveness of the bars for controlling cracks.
In order to find the basic fatigue properties of reinforced concrete, the authors have been engaged in making, for several years, the fatigue test with various kinds of reinforced concrete beams having different types of failure. In this paper, the diagonal tension fatigue test is mainly dealt with. The test beams were made of both lightweight aggregate concrete and normal concrete. The result obtained from this test is discussed, and compared with the one obtained from the test of beams having another type of failure. It was interesting to notice that no matter of whatever type the failure was, nor any matter whatever kind of concrete was used, the same percentage of fatigue endurance of beams to their static endurance was obtained in these fatigue tests. Failure occurred more suddenly in the beams made of lightweight aggregate concrete than in the normal reinforced concrete beams. Wherever the beams made of lightweight aggregate concrete are employed, therefore, efficient reinforcement construction to diagonal tension is indispensable.
The purpose of this investigation is to clarify the basic behavior of the simply supported prestressed lightweight concrete beams under quasi-static loading with once removal of load preceding the final failure. The prediction method of moment-curvature relationships of beams is also discussed. Ten post-tensioned grouted prestressed concrete beams with the uniform eccentricity of tendons and the accompanying concrete test cylinders (φ10×20cm) were employed in this study. The test beams were loaded at the third points of the span. The test program includes two beams with monotonously increasing load and six beams under the loading with once removal of load near failure. The start of unloading was controlled by the compressive extreme fiber strains in the bending span of the test beam, ranged from 1.9‰∼2.8‰. The residual and ultimate strains in the compressive extreme fiber of the beams have no relation with the amount of their compressive strains at the beginning of unloading. The ultimate rotation strains, the failure strength and the initial bending stiffness at the beginning of reloading do not deteriorate due to the load history including once unloading. It is found that the relations of the bending stiffness to the bending moment in the repeated cycles are simply represented as bi-linear relation from the experimental curves according to the index of the compressive extreme fiber strains of concrete prior to unloading. Using this relation, the bending moment-curvature curves under the loading with such removal of load are predicted with accuracy.
This report describes the results of experimental studies made on the design method for composite prestressed concrete beams, the flange or the upper portion of which was placed with concrete using the lightweight aggregate on the precast prestressed beam made with normal weight aggregate concrete. Thirty beam specimens were fabricated in all, and the variables involved in the specimens were as follows; the shape of the cross section, the amount of shear connector, the ratio of the shear span to the beam depth and the age of casting slab portion. Investigation was made of the deformation characteristics, the crack, the differential shrinkage set up and its effect on the cracking strength, the shear strength of the bonded surface, the ultimate strength, and other characteristics of the composite prestressed concrete beams, and these were compared with their respective theoretical analyses. The main results obtained are as follows. (1) The recovery of deformation of the composite beams is as complete as in the ordinary prestressed concrete beams, so long as no harmful slip is formed. (2) The differential shrinkage has so profound effects on the cracking strength that it should be taken into consideration in the design, especially when the slab concrete is placed later. (3) The ultimate flexural moment can be calculated by the same method as is used for ordinary prestressed concrete beams. (4) When the slip on the bonded surface increases suddenly, the resisting shear stress reaches its maximum.