Shigeyuki Date

Combined Effect of Thermal Stimulated Superplasticizer with BFS on Fresh and Hardened Property of Mortar

Usage of mineral and chemical admixtures in concrete or mortar is a usual solution to reach full compaction mainly where reinforcement blockage and the shortage of skilled labors happen. Super Plasticizers have become essential ingredients of any designed concrete mix today. Property of fresh and hardened concrete is strongly influenced by the interaction of mineral and chemical admixtures. This paper has been made to evaluate effect of heat stimulation of with two types of Polycarboxylic acid-based ether superplasticizer, pre-cast (SP2) type and ready-mix (SP1) type superplasticizer (SP) with normal Portland cement (OPC), high early strength cement (HESPC) and partially replacement of blast furnace slag (BFS) with cement 0%, 30%, 45%, and 60%. Investigated the fresh and hardened property of mortar. The superplasticizer (SP) was heated in a thermostatic chamber 70°C for 24 hours, the result shows that the heat stimulation of SP increased the fluidity, air content and flow loss, and decrease the density and compressive strength of mortar. Consequently, unitized the flow for heated and non-heated SP, and evaluate them. The air-content, density, and compressive strength were same. Besides, the flow loss was affected by many factors type of cement type of SP and heat stimulation technique of SP amount of BFS. By heat stimulation technique and increasing the amount of BFS caused to decrease the flow loss. The SP1 improve the fluidity and flow loss of mortar than SP2 in all conditions. Heat stimulation technique of SP with HESPC cement doesn’t change the fresh property of mortar. The compressive strength of HESPC was increased than OPC cement. Furthermore, by increasing the amount of BFS increased the fluidity and decreased the compressive strength and effect of heating on fluidity. The water-cement ratio was 30% and sand cement ratio was 2:1. Blast furnace slag (BFS) cause to improve the fluidity of mortar. However, by increasing the amount of BFS the compressive strength and effect of heat stimulation and flow loss was decreased.

Effect of Expansive Additive and Shrinkage Reducing Agent on Plastic Shrinkage of Steam-Cured Mortar

This research is part of the mortar’s plastic shrinkage study. Contents in this article is related to how the Expansive Additive (EX), Shrinkage Reducing Agent (SRA), and Fly Ash (FA) help to reduce and control the shrinkage and to compare the effectiveness of these substances used in the normal curing, i.e., at 30 °C and in the steam curing process by using the factorial design with 3 factors and to be divided into 2 levels. Factors to be studied are the amount of EX, SRA and FA replacement. The test of plastic shrinkage was conducted in accordance with the ASTM C1579-06 standard, placing the strain gauge 0.5 centimeters beneath the surface in the middle of the mold, recording the shrinkage rate starting from the initial setting time for 24 hours. The results showed that, in normal curing, the EX influences the expansion while, in steam curing, the EX and SRA significantly influences the expansion. To add the FA in high volume along with the EX significantly effects the expansion for both the normal and steam curing. Furthermore, the study model and equation for plastic shrinkage of mortar are presented in the form of factor proportion to be considered from the factorial design study basis.

Study of Productivity Improvement on Precast Concrete by Calcium Silicate Hydrate Type Accelerator

The effect of early strength improvement of concrete with C-S-H type accelerator was studied for precast concrete efficient production under the steam curing condition. From the mortar test result, the effect of this improvement was confirmed to tend lager as the W/C is lower. This accelerator could short the curing time for 0.5-2.0 hours under the same temperature condition, and could reduce the curing temperature under the same curing time. Then the compressive strength was considered to be predicted by some formula, and it showed higher estimation accuracy of the Arrhenius’s Law than that of the Maturity Method.

Influence of Replacement Rate of Fine Aggregate by Blast Furnace Slag Sand on Fresh Properties of Mortar

For enlarging and promoting usage of blast furnace slag sand and improving construction performance of concrete with it, the behavior of the mortar under both static and dynamic, using vibrator, conditions were confirmed from the viewpoint of plastic viscosity, filling property and bleeding rate. As the results, within the scope of this experiment, by investigating the mixing ratio at which the plastic viscosity changes from the vibration plasticity viscosity obtained by the feather penetration type viscosity measurement test, it was considered that the appropriate fine aggregate mixing ratio can be estimated. Furthermore, the pore water pressure was measured for a sample in which the mixing ratio of the fine aggregate was changed, and the possibility of evaluating the fresh properties from the tendency of disappearance of pore water pressure after stopping the vibration was indicated.

Effect of Type of Cement and Expansive Agent on the Hardening of Steam-Cured Concrete

Pre-cast concrete products are sometimes manufactured in two cycles daily. It is ensured that they have the required strength at an early stage of demolding by increasing the steam curing temperature to reduce cost or increase productivity. However, the reduction in durability because of cracking due to thermal stress is a topic of concern. On the other hand, it has been known that fine blast-furnace-slag powder and expansive agents show high temperature dependence. Although they are used even in precast concrete products, the effect of steam curing on these materials is not known. Thus, in this study, the expression of compressive strength and expansion that are critical in improving the quality and productivity of precast concrete products was investigated, using high early-strength cement and two types of expansive agents, namely, ettringite-based and lime-based agents. Consequently, the strength expression was accelerated by the addition of expansive agent to ordinary cement and high early-strength cement. The extent of restrained expansion is greater for the lime-based expansive agent than for the ettringite-based expansive agent, and when an expansive agent is added to high early-strength cement, the extent of restrained expansion falls to a level lower than that in the case of ordinary cement.

Discussion of Mix Proportions of Concrete for Long-Distance Pumping

Long-distance pumping of concrete (up to 2000 m, with relay pumps installed at two locations) was carried out for placing invert concrete at a caisson—the construction site of a spillway discharge section. After quantifying the required performance and determining of the mix proportions of the invert concrete that would be used in the long-distance pumping, the authors focused on thixotropy as a factor that affects the pumping load. Through laboratory tests and using AE and a high-range water reducing agent with high dispersion effect, retention and pumpability enhancing admixture were found to be effective in reducing thixotropy.

Effects of curing conditions and addition of fine blast furnace slag powder on the initial performance of concrete using expanding material

In this study was investigated the effect of steam curing in the case of adding expandable material to powdery high fluidity concrete containing blast furnace slag fine powder on two kinds of expansive materials, ettringite type inflation material and lime type expansion material. As a result, the constraint expansion strain increases with the ettringite type due to the increase in the steam curing temperature. However, it was confirmed that it decreased with the lime type expansion material.

Effect of setting accelerator to the initial strength of mortar with blast furnace slag cement

Effect of three types of setting accelerators such as calcium nitrous, calcium nitrate and C-S-H micro crystal dispersion on early strength enhancement of mortar with blast furnace slag cement were investigated. As a result, it was confirmed that compressive strength of mortar at early age had been enhanced by each accelerator, among them, the accelerator of C-S-H type showed the highest promoting effect. Furthermore, it was found that when the dosage is 4% or more, the initial strength designated by construction procedure can be secured and the productivity of construction work can also be improved.