This paper describes the effects of properties of binding material (specific surface, solid volume percentage and etc.) on the plastic viscosity of fresh paste with admixtures. Eight types of binding material and three types of high range water reducing agent were used, and the plastic viscosity of paste with these materials was measured, keeping the yield value of paste constant. The fresh paste is considered to be a type of high concentrated suspension. So the authors propose a prediction method of plastic viscosity on this concept. In this method, the ratio of binding material content, the specific surface and solid volume percentage of binding material, the type of admixture and others are taken into account as the factors.
Recently in Japan, the demand for low heat cement to prevent thermal cracks is growing higher because of scaling up of concrete structures. Usually, moderate heat portland cement and binary or ternary blended cement in which ground blast-furnace slag and fly ash were admixed have been used as low heat cement. However, such blended cements have several problems. For examples, the heat of hydration of moderate heat cement is not sufficiently low. The quality of blended cement is not stable and it is very difficult to control and stabilize its quality because of incorporating industrial by-products, and the rate of carbonation is quite fast. Therefore, belite-rich cement is expected much as low heat cement which is more durable and effective to prevent thermal cracks. In this study, the effect of the content of belite in cement on the property of concrete was investigated by using four kinds of belite cements in order to make the characteristics of belite-rich cement clear. The relations between the replacement ratio of blast-furnace slag and adiabatic temperature rise or strength were also investigated using belite-rich cement containing about 60% of C2S, under the condition that the replacement ratio of fly ash was kept 30% constant.
The purpose of this study was to scrutinize the basic properties of ordinary portland cement concrete which contains blast-furnace slag granulated finely to such a degree as having a specific surface area of 4000 to 10000cm2/g by blaine, and then to clarify an appropriate method of applying the blast-furnace slag to concrete. In the experiment the ratio of cement replacement with the ground granulated blast-furnace slag was 30, 50, or 70%, the ratio of water to the cement plus ground granulated blast-furnace slag 35, 45, or 55%, the slump 18±2.5cm, and the air content 3-5%. Many useful data were obtained, and it was clarified that, when used as an additive for concrete, the fine granulated blast-furnace slag could provide the concrete quality that meets the purpose of application by selecting the ratio of cement replacement with the slag and fineness of the slag.
Atmospheric pressure steam curing has been widely used for precast concrete products, as the high curing temperature accelerates early concrete strength development. Though steam curing has an economic advantage over ordinary moist curing, it has one problem that should not be ignored. Sometimes fine cracks are formed on the surface of precast concrete products. It has been proposed that these fine cracks are formed during a certain stage of steam curing. The purpose of this investigation was to reveal the condition and mechanism of fine crack formation on the surface of steam cured concrete. A new X-ray technique, using a contrast medium, was developed and used to detect fine cracks on the surface of concrete. As a result of the study, three different types of fine cracks, namely mortar cracks, vapor cracks and separation cracks between aggregates and pastes were observed. They occurred at different stages of steam curing. The condition of developing cracks was also studied and compared with the standard specification of the Japan Society of Civil Engineers.
The thin wall of a pre-stressed concrete LNG storage tank is very intricate with many reinforcing bars, sheaths and other steels, and it is very difficult to fill it up with concrete. So, for the construction of the wall of the structure, it is compeled to apply the inverse casting method by using high performance concrete, which has high strength, high endurance, high workability and non shrinkage. This report describes the results of the experimental study on a high performance concrete and its practical use to actual structures, in order to find the details as followings: (1) The limit of the unit coarse aggregates upon filling capacity of concrete. (2) The effect of low heat type cement upon controlling thermal stress. (3) The effect of expansive admixture and aluminium powder upon volume stability.
Recently, a number of bridge concrete piers which appear to be damaged by the alkali-silica reaction, have been found in a certain district in Japan. The major purpose of this study is to reveal whether the damage in the concrete piers was caused by an alkali-silica reaction. Another important problem is to predict the residual expansion capacity of the affected concretes for the purpose of repairing them appropriately. The reactivity of aggregates used in the concretes was investigated by microscopic examination. In this district, a large amount of sodium chloride is being used as a deicing agent for many years. Accelerated expansion tests in saturated NaCl solution as well as in high humidity were carried out to predict the residual expansion of the actually damaged concrete piers. The correlation between the results obtained by the accelerated expansion tests in saturated NaCl solution and in high humidity was found to be considerably good. Andesitic and rhyolitic aggregates in the concretes were reacting.
In reinforced concrete structures, the degree of deterioration due to an alkali aggregate reaction is influenced by the amount of reinforcement in the concrete, because the reinforcement restrains the expansion due to the alkali aggregate reaction. To investigate the effect of reinforcement steel on the deterioration of concrete, experimental works were made using concrete prism specimens with various amounts of steel reinforcement. Expansion and crack patterns were measured for 2 years. And the compression tests of the concrete prism specimens were caried out after 5 year's storage. Compressive strength, stress-strain relationship and Young's modulus were measured for each specimen. At the same time, acoustic emission characteristics of each specimen during compressive loading were investigated. The test results show that the deterioration of concrete due to the alkali aggregate reaction decreased extremely when the steel reinforcement ratio was more than 0.71%. One of the reasons is considered that the growth of cracks is restricted by the chemical prestress induced in the concrete with the expansion of concrete due to the alkali aggregate reaction, resulting the decrease of water supply to the inner part of concrete.
A total of five ferro-nickel slag fine aggregates were examined by blending natural fine aggregates to investigate the freeze-thaw resistance of concrete with these fine aggregates. The volume blending ratio of slag fine aggregates in excess of 60% resulted in poor freeze-thaw resistance of concrete when the water cement ratio exceeded 55% and the air content less than 5%. The inherent freeze-thaw resistance of slag sand particles was superior to that of natural fine aggregates. The poor resistance of concrete with slag fine aggregates couldn't be well explained by the air content and spacing factor. The major cause to impair the resistance was guessed the excess bleeding and it was found that the larger the amount of bleeding, the poorer the freeze-thaw resistance of concrete. It was concluded that the durable concrete could be produced by suppressing the bleeding less than 0.4cm3/cm2 together with the suitable air entrainment.
The deterioration caused by freeze-thaw action seems to develop gradually from the surface to the inner part. When the frost damage is limited in the cover, the weakened portion is chipped off and the recovering is made by using some repairing material. In this case, it is very important to make a perfect removal of the weakened portion, but its thickness is usually determined empirically by the chipping force and so on. In this study, experimental investigations were made on the assessing technique to the thickness of damage portion and on the performance of repairing materials to bond tightly on the concrete surface and to protect it from the frost damage. The degree of damage at different levels of depth was assessed fairly well from the mechanical degradation by applying the improved pull-off test method. The rebound number and depth of pin penetration could be also used as its measure. The rapid air permeability and water absorption tests were useful for getting the information on the changes of air and water tightness caused by the deterioration due to freeze-thaw action. By using two kinds of repairing material in nine different repairing procedures, the performance after repair was examined to evaluate the refraining effect from suffering the subsequent damage. Furthermore, four types of surface coating material were examined and their ability to prevent the freeze-thaw damage was experimentally confirmed.
At present, conventional concrete has such a image as “heavy, hard, cold”, and has many problems about durability and thermal insulation. And the shortage of natural aggregates has become a serious problem. Thereupon, the authors have developed a special lightweight concrete (MLC) by using formed polystyrene beads with a diameter of less than 1.5mm as an aggregate having no water absorbability. MLC with a low water-binder ratio is an excellent lightweight concrete having excellent properties of durability and thermal insulation. This paper reports the performance of this special lightweight concrete.
Polymer mortars such as polyester, epoxy and polymethyl methacrylate mortars are widely used in the construction industry. The polymer mortars are prepared by use of polymeric binders, fillers and aggregates, and the properties of the polymer mortars are considerably affected by the properties of polymeric binders used. A main component of the binder for the polyester mortar is unsaturated polyester resin. Styrene monomer as a diluent is sometime added to the binder. However, the strength of the polyester mortar is decreased when much styrene monomer is added. On the other hand, methyl methacrylate monomer as a main component of the binder for the polymethyl methacrylate mortar requires some crosslinking agents to improve the strength properties of the mortar. The unsaturated polyester resin can be added to the binder as an ingredient of shrinkage-reducing agent for the binder. In the present paper, the combined use of an unsaturated polyester resin and vinyl monomers as the binders for polymer mortars is examined. Styrene monomer or methyl methacrylate monomer with and without a crosslinking agent is added to the unsaturated polyester resin to prepare the binders for the polymer mortars. Basic properties such as working life, strength, stress-strain relationship in compression and modulus of elasticity of the polymer mortars are discussed. In conclusion, such basic properties of the polymer mortars are markedly affected by the formulations of the binders used. In the formulations of the binders, the combined use of the unsaturated polyester resin and methyl methacrylate monomer is found to be reasonable rather than the combined use of the unsaturated polyester resin and styrene monomer.
The carbon fiber-reinforced plastic (CFRP) plate bonding is a method in which CFRP plates are bonded by mean of epoxy resin to the surface of existing reinforced concrete (RC) structures. This method permits the insufficient amount of steel bars in the section of the structural member to be compensated externally. Therefore, it is considered that this method will become widely used under a corrosive environment since the CFRP plate is rust-proof. In this study, the strength and deformation characteristics of the RC beam strengthened with a CFRP plate under static and fatigue loading were dealt with. The experiments revealed the mode of failure for the beam bonded with a CFRP plate and subjected to static incremental loading to be flexural failure, and both the flexural rigidity and ultimate strength to increase. The fatigue failure for the beam bonded with a CFRP plate under the repetitive loading was not produced by the fatigue fracture of CFRP plate but by that of steel bars. The fatigue strength at 2×106 cycles of load repetition for the RC beam bonded with a CFRP plate was 57 percent of the static strength of the same beam.
Design concept for reinforced concrete slab structures subjected to impact load based on energy and load criteria is studied in this paper. Firstly, the evaluation of impact resistance for reinforced concrete handrails which were modeled using the layered finite element method, is proposed based on a few indexes. The effect of impact loading on several types of reinforced concrete handrails based on these indexes is discussed quanititatively as well as qualitatively. Next, design concept for reinforced concrete slab structures based on a dynamic analytical procedure is suggested. The energy criterion as well as load criterion are considered in the design procedure under impact load. Moreover, the indexes for impact resistance are employed for determining structural modification necessary in the design procedure.