The deterioration of concrete by sulfuric acid attack in sewage environments has become a serious problem for many existing sewage structures. By using the blast furnace slag fine aggregate and blast furnace slag fine powder, it is possible to enhance the resistance to sulfuric acid of mortar and concrete. When mortar or concrete reacts to sulfuric acid, the gypsum film is formed around the surface of concrete. This gypsum film could retard the penetration of sulfuric acid, thus improving the resistance to sulfuric acid. Higher compressive strengths of ordinary concrete yields lower resistance to sulfuric acid. By using the blast furnace slag sand as a fine aggregate, a high compressive strength concrete also has a high resistance to sulfuric acid. Furthermore, it has been proved that that the relationship between the corrosion depth by sulfuric acid attack and the product of immersion period and concentration of sulfuric acid can be expressed by linear. This relationship is independent of the type of materials of concrete.
This study aims to evaluate an effect of the γ-C2S and Quartz substitution ratio to OPC, on the sulfuric acid resistance in autoclaved cementitious materials, such as paste, mortar and concrete. Furthermore, to evaluate the application of a laboratory test, comparing an actual environment testing to an accelerating test in a laboratory has been carried out. As a result, in case of quartz substitution ratio 50% and γ-C2S substitution ratio 40% with autoclaved curing, the high sulfuric acid resistance obtained. Because the sulfate ion penetration was inhibited due to silica gel and C-S-H gel produced by resolutions of tobermorite or residual γ-C2S at the surface part. Also, accelerating test in a laboratory is useful comparing an actual environment testing. Because the accelerating test in a laboratory and the actual environment testing show the same tendency.
Drying shrinkage of concrete is a phenomenon caused by moisture distribution of concrete. Moisture distribution of concrete causes because evaporable moisture transfers from inside to outside of concrete through the drying surface. The drying shrinkage near the drying surface is much bigger than that in the center of concrete at arbitrary drying time. However, when the ratio of the length to the thickness of concrete member is high such as a prism test specimen (100×100×400mm) or a bridge girder, the Navier hypothesis is applicable for the deformation due to drying shrinkage and the longitudinal total strain both drying shrinkage and elastic strain is consequently constant at any place in the section. In general, the time-dependent strain due to drying shrinkage can be expressed by the hyperbolic equation. In other words, the time-dependent strain due to drying shrinkage with the lapse of time is expressed by two parameters, that is, the parameter for ultimate drying shrinkage strain and the parameter to express the change of strain by the lapse of time. In this study, the method to predict the drying shrinkage strain in full-scale structures by using drying shrinkage obtained by test according to JIS A 1129 test is proposed. As a result, it is shown that the parameter to express the change of strain by the lapse of time is proportional to the square of the representative member thickness.
There are a few cases that cracks occurred on PC structures at their young ages. It is judged that cracks were caused by large drying shrinkage of concrete. Drying shrinkage strain develops with the loss of moisture. When drying shrinkage is assumed to be constant at any position of cross section, it is impossible to simulate the crack due to drying shrinkage strain. The reason is that internal stress in concrete is developed by the difference of drying shrinkage between inside and outside of concrete. In order to examine the influence of the internal stress, the moisture distribution in concrete is calculated according to the diffusion equation. The analysis in this study targets to the PC bridge in site. As a result, it will be shown that internal stress of the PC bridge can be simulated and that the effect of drying shrinkage on the crack of the PC bridge can be presumed.
This paper discusses the suppressing mechanism of supplementary cementitious materials (SCM) for expansion by alkali-silica reaction from the viewpoint of phase composition of cement hydrates. Hydration process and phase composition of hydrated cement paste were analyzed by using combined XRD/Rietveld analysis and chemical analysis. Suppressing effect of SCM was evaluated by mortar bars with 1.2% alkali and 40°C. Additionally, hydroxide ion concentration in pore solution was estimated based on the chemical composition of C-S-H gel. As the results, incorporating SCM contributed to the reduced Ca/Si ratio of C-S-H gel. The suppressing effect of SCM was correlated with the hydroxide ion concentration. These results strongly suggest that the mechanism of SCM for suppressing ASR expansion can be attributed to the reduction in hydroxide ion concentration in pore solution.
Drying shrinkage of concrete affects on the deflection, cracking, loss of prestress and so on of concrete member. It is important to predict the effect of drying shrinkage in design due to take the safety, serviceability, durability and so on of concrete structure into consideration. It is, however, difficult to obtain the data of drying shrinkage at the stage of design. Because the specification of concrete or even concrete manufacturer are not selected. Furthermore, it takes much time to obtain the data of drying shrinkage by experiment. That is why the prediction equation for drying shrinkage strain established by experiment data obtained in each country is used in generally. In this study, the prediction equation of drying shrinkage strain measured by 100×100×400mm prism specimen is proposed by using some data obtained in Japan. The data measured two years ago and the data measured thirty years ago were used. The comparison of these two types of data shows the effect of the quality change of an aggregate on drying shrinkage strain. The new prediction equations proposed in this study includes the effect of type of aggregate by the term of moisture content of aggregate. Furthermore, in the actual structure, the development of drying shrinkage strain becomes slower because of the effect of member size and the ultimate drying shrinkage strain becomes smaller because of the effect of temperature history in curing are shown.
In this research, the authors used element test samples which modeled actual structures, to consider a quantitative method for evaluating the internal vibrator insertion intervals and compaction times necessary for concrete used in construction, based on the concrete compaction completion energy, using concrete slump as a parameter. The following conclusions were reached. The theoretical compaction completion ranges calculated from compaction energy were almost identical to the actual compaction completion ranges of elemental tests modeled on actual structures. It is difficult to evaluate the degree of compaction purely through visual evaluation of the cast condition of the form surface, and doing so is risky. In follow-up compaction, even if compaction time gets longer properly, quality does not have any problem.
Recently, infrared thermography measurement is focused as a effective and economical method of maintenance and management for structures because more and more structures are aging. In-situ application of the measurement has been increasing year by year in civil engineering and there are many researches on influence of measuring environment. However, it is important not only to detect spalling area but also estimate risk of spalling for selecting effective repair method. In this study, in order to estimate risk of spalling crack, infrared thermography measurement was carried out for specimen damaged by experiment simulating reinforcement corrosion. As a result, we suggest spalling risk as an effective index which isn't influenced by cover thickness or failure pattern, and clarify that it is possible to predict time to spalling by measuring thermal temperature.
The safety of reinforced concrete (RC) structures for shear force is verified by confirming that shear force does not reach the design shear capacities (Vyd, Vdd). Based on experimental results, Vyd and Vdd have been obtained which are expressed as a function of shear-span to effective depth ratio (a/d). Therefore, significant difference between Vyd and Vdd at a/d =2.0 occurs in the case of RC beam having larger shear reinforcement ratio. One of the reasons is that the contribution of stirrups on the shear capacity of RC beams has not been clarified. Based on 611 experimental results, this research has investigated the contribution of stirrups and loading plates on the shear capacity of rectangular cross-sectioned RC beams. Finally, calculation method of the design shear capacity for RC beams ensured continuity to a/d was proposed.
This paper shows the results of 23-year outdoor exposure test of concrete specimens made with 94 aggregate collected from various area of Japan. ASR risk of rock types in Japan is discussed with the data of cracking of exposed test specimens, test results of alkali-silica reactivity of aggregate by chemical method (JIS A 1145) and mortar-bar method (JIS A 1146). Results of exposure test of concrete specimens whose Na2O equivalent alkali content was 5.0kg per cubic meter, basically reconfirms the existing knowledge of alkali-silica reactivity of Japanese aggregate. For instance, post-Miocene volcanic rocks in Japan are frequently reactive. On the other hand, cracking due to ASR was occurred in some concrete specimens made with pre-Miocene volcanic rocks and hypabyssal rocks though these types of rocks in Japan has been thought to be non-reactive. In these cases, it is estimated that late-expansive ASR has occurred and test results of alkali-silica reactivity of aggregate by chemical method and mortar-bar method was not suitable. Cracking of concrete specimens are also observed in low-alkali concrete whose Na2O equivalent alkali content was 3.0kg per cubic meter.