Concrete Research and Technology

Effects of Reinforcing on Damage of Reinforced Concrete Slabs subjected to Explosive loading

Hideaki TANAKA, Masanori TUJI

2003 Volume 14 Issue 1 Pages 1-11
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_1

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In this study, effects of reinforcing on the damage of reinforced concrete slabs subjected to Explosive loading has been experimentally investigated to improve the design and damage estimate methods of reinforced concrete structures. Explosive Pentolite were detonated on the surfaces of seven kinds of reinforced concrete labs, with different reinforcement. After the tests, the damage in the slabs was observed in detail and analyzed for the crater, spall, breach and crack. The tests results showed that reinforcing using steel net or high ratio of steel bars in reinforced concrete slabs are slightly effective to prevent the damage of crater and spall depth, but aren't to prevent spall perfectly, and so on.

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Shear Strength of PC Beams with High Strength Lightweight Aggregate Concrete

Hiroshi Watanabe, Hirotaka Kawano, Masahiro Suzuki, Shigeto Satoh

2003 Volume 14 Issue 1 Pages 13-22
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_13

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This paper reports on the shear strength of PC beams with high strength lightweight aggregate concrete. Shear cracking strength of RC beams with lightweight coarse aggregate and lightweight sand is remarkably smaller than that with normal weight concrete. Usage of lightweight aggregate also reduces concrete contribution for shear strength after shear cracking. Shear cracking strength and ultimate shear strength of concrete increased with the amount of prestressing force. The type of aggregate seemed to have no influence on the amount of increment of shear cracking strength by prestressing.

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Autogenous Shrinkage Strain Properties of Portland Blast-furnace Slag Cement Concrete Taking Account of the Heat of Hydration

Katsuki HARADA, Hiromichi MATSUSHITA, Takahiro GOTO

2003 Volume 14 Issue 1 Pages 23-33
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_23

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Early-age autogenous shrinkage strain and stress of portland blast-furnace slag cement concrete were determined taking account of the heat of hydration. When moderate-heat cement and low-heat cement were substituted with ground granulated blast-furnace slag, the strain turned into shrinkage under an increase in concrete temperature. This may be attributed to an autogenous shrinkage accelerated by a rapid decrease in pore spaces as a result of ettringite conversion into monosulfate.The autogenous shrinkage was able to be reduced by increasing the SO₃ content of low-heat portland blast-furnace slag cement.It was found by the cement paste experiments that the strain reversal was most affected, among characters of the portland blast-furnace slag cement, by the blaine value, degree of substitution and type of the base cement. The autogenous strain stress showed considerable increase at high ambient temperatures (35°C) than at a room temperature (20°C).

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Effects of Mix Proportioning Factors on Basic Properties of Polymer Mortars Using Waste Expanded Polystyrene Solution-Based Binders

Nakwoon Choi, Yoshihiko Ohama

2003 Volume 14 Issue 1 Pages 35-41
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_35

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The purpose of this study is to develop an effective recycling method for waste expanded polystyrene (EPS). Polymer mortars using the binders based on a styrene solution of the waste expanded polystyrene are prepared with various binder contents, crosslinking agent contents and coupling agent contents, and tested for consistency, working life and mechanical properties. As a result, the workability of the mortars are improved with increasing binder content and crosslinking agent content, and their working life is shorten with an increase in the crosslinking agent content. Their flexural and compressive strengths depend on the crosslinking agent content and coupling agent content, and their modulus of elasticity is greatly affected by the binder content. In general, the mechanical properties of heat-cured mortars aremuch higher than those of dry-cured mortars.

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Study on Properties and Mix Design of Self-Compacting Concrete Containing High Volume Fly Ash

Takeshi Narita, Kazuo Sekino

2003 Volume 14 Issue 1 Pages 43-56
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_43

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In self-compacting concretes containing fly ash, the upper replacing ratio limit of fly ash to a cementitious material has been stipulated by the Japan Society of Civil Engineers (JSCE) and the Architectural Institute of Japan (AIJ). This study investigates the proposal of the mix design, the effect of the replacing ratio of fly ash on the strength and the durability of concretes complied with the self-compacting rank 2, and the ability of construction according to practical construction work from the viewpoint of the effective uses of fly ash. The results obtained are as follows : The strength and the durability of the self-compacting concretes containing high volume fly ash are influenced by various replacing ratio of fly ash. The self-compacting concrete at 50% of the replacing ratio is excellent workability and compaction at the site of construction.

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A study of the strength recovery of mortar with an initiated crack

Hiromichi Matsusita, Yoshihiro Sue, Rie Kiyosaki

2003 Volume 14 Issue 1 Pages 57-65
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_57

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Initial crack in concrete structure is mentioned as a factor which lower durability. Then, the purpose is an index of a crack test in the ability test type. In this study, three point bending test of mortar with a crack initiated was carried out, and strength was examined. The factor was the type of cement, the time of crack initiated, and the curing period. The system of the strength recovery is the hydration of the unhydrated cement at the initial crack

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Fluidity Retention Effect of Slowly Cooled Blast Furnace Slag Powder and Its Mechanism.

Minoru MORIOKA, Takayuki HIGUCHI, Kenji YAMAMOTO, Etsuo SAKAI

2003 Volume 14 Issue 1 Pages 67-74
Published: January 25, 2003
Released on J-STAGE: November 13, 2012

DOIhttps://doi.org/10.3151/crt1990.14.1_67

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It was found that the self-compacting concrete added with the slowly cooled blast furnace slag powder has a better property of fluidity retention than the self-compacting concrete added with the granulated blast furnace slag powder or the lime stone powder. As for the mortar added with slowly cooled blast furnace slag powder, the greater the Blaine specific surface is, the better the fluidity retention is obtained. The fluidity retention mechanism of the ordinary portland cement - slowly cooled blast furnace slag powder system was shown to be resulted from that the initial hydration of C₃A is suppressed by the thio-sulphate ion released from the slowly cooled blast furnace slag powder

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