This paper describes experiments and numerical simulations on the influence of weather actions such as temperature and humidity, precipitation, and solar radiation on the drying shrinkage of concrete. The test specimens casting at the same time were exposed at four outdoor locations in Japan and were measured the time-dependent change of water content and shrinkage strain. Experimental results showed that the shrinkage strain for one year was almost the same in each experimental location, but the progress of shrinkage in each season was different. By examination using the numerical simulation of moisture transfer and shrinkage strain of concrete that can consider the influence of temperature and humidity fluctuations, solar radiation, and precipitation, it was revealed that humidity fluctuations and rainfall had a great influence on the shrinkage behavior. A coefficient to consider the influence of humidity fluctuation and rainfall was calculated from the average humidity and the ratio of rainfall time, and the apparent relative humidity was calculated by multiplying the average humidity by the coefficient. It was shown that the shrinkage strain of concrete outdoors can be easily predicted by using JSCE shrinkage prediction formula which applied apparent relative humidity.
The authors evaluated the spalling of polymer cement mortar (PCM) restrained by a steel ring in high temperature. The polymer cement mass ratio (P/C) was 20%. In addition, a specimen of ordinary cement mortar was used for comparison. The spalling test by the ring restrained specimen measured the internal temperature, restrained stress and water vapor pressure. The spalling scale after heating was graded based on the spalling depth distribution on the heated surface of the ring restrained specimens. The heating conditions were the RABT30 heating curve. The tensile fracture strain was calculated from the restrained stress at the time of spalling of PCM and NCM specimens. Furthermore, P/C and tensile fracture strain are shown by relational expressions. From this equation, the time which tensile strain fracture of PCM with P/C=5 to 20% occurred was estimated. As a result, it almost same the time when the spalling occurred. When PCM spalling occurred, the restrained stress caused tensile strain fracture of the mortar and a sharp decrease in water vapor pressure. On the other hand, the specimens made of polymer cement mortar mixed with nylon fibers stopped spalling during heating. In PCM mixed with fibers, gaps were created at the interface between fibers and PCM and by melting of fibers at high temperature. Water vapor moved into these gaps, and the vapor pressure was relaxed, causing the spalling to stop.
The purposes of this study are to develop sewer pipes with cementless mixtures (IBPM) and to use IBPM as material for various types of precast concrete products. The IBPM mixture includes four types of industrial byproducts consisting of fly ash, ground granulated blast-furnace slag, granularity controlled sewage sludge incineration ash and silica fume. Calcium hydroxide and expansive additive are also added as an alkali stimulant and shrinkage reducer, respectively. Strength development of mortal with IBPM with different proportions were evaluated. An actual sized specimen of sewer pipe with IBPM was also produced at a precast concrete plant and hydraulic tests to measure the roughness coefficient of the inside surfaces of the pipe. As a result, it was found that strength development of steam-cured IBPM concrete was adequate for precast concrete produces with compressive strength of 40 N/mm2. Reinforced concrete beam with IBPM concrete made by steam curing demonstrated almost the same load-bearing performance as those with cement concrete. It was also proved that sewer pipe with IBPM concrete had good flow capacity with similar roughness coefficient as vinyl pipe.
This study presents a kinematic model for ﬂexural analysis of RC linear members subjected to freeze-thaw action based on upper bound theorem. The developed model enables analytical derivation of the contribution of damaged concrete when a velocity ﬁeld is divided into undamaged and damaged zones based on freeze-thaw depth obtained from concrete core specimens. The accuracy of the model is veriﬁed by comparing its predictions with available 21 RC columns and beams failing in ﬂexure after freeze-thaw exposure. The predicted results show very good agreement with the test results within error of 5% on average. Thereafter, the developed model predicts the ultimate moment of an existing RC beam, which was out of service because of combined effect of frost damage and fatigue. Close agreement is observed between test results and analytical predictions.
Internal loading method (ILM) has been proposed as a evaluation method for the strength of buried pipes. The purpose of this method is to evaluate the deterioration of a pipe or backfilling soil from the relationship between load and deformation of a buried flexible pipe by loading from the inner surface. On the other hand, flexible pipes account for about 90% in the extension of agricultural pipelines, and application of this method to flexible pipes is particularly required. In this study, the effect of overburden pressure on the behavior of the pipe was investigated by installing a VU pipe into the model ground with different earth pressure under ILM. As a result, with lager earth pressure, the inclination of load-deformation curves became larger, and the curve lines turned to linear. In addition, the inclination of buried VU pipe under repeated loadings, became larger at the second and subsequent loadings than the first loading. It was thought that the soil stiffness had increased by the stress history of the first loading.
This study focuses on the tension stiffness of reinforced concrete members, which is significant for predicting time-dependent of crack width and deflection of reinforced concrete members. The influences of sustained load and drying on reinforced concrete members were clarified through systematic uniaxial tension tests on reinforced concrete members in which drying shrinkage before loading, sustained load, and combination of sustained load and drying shrinkage were investigated. The values of strain representing the influences of shrinkage and creep in the formula of crack width by Japan Society of Civil Engineers standard specification were reassessed by similar strain based on the test results.