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International Concrete Abstracts Portal

Showing 1-5 of 265 Abstracts search results

Document: 

19-158

Date: 

September 1, 2020

Author(s):

Faez Sayahi, Mats Emborg, Hans Hedlund, and Andrzej Cwirzen

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This research studies the effect of retarder, accelerator, stabilizer, air-entraining agent, and shrinkage-reducing admixture (SRA) on plastic shrinkage cracking in self-consolidating concrete (SCC). The main objective is to identify the dominant cracking cause—that is, plastic settlement or plastic shrinkage—in an SCC containing a particular admixture. During experimentation, crack-free concretes were achieved by adding air-entraining agent and SRA, while accelerator and retarder increased the crack area. The impact of admixtures on the cracking mechanism was identified by comparing the respective vertical and horizontal deformations. It was observed that the crack-free concretes had moderate settlement and horizontal shrinkage, while the cracked specimens exhibited significant deformation either vertically or horizontally.

DOI:

10.14359/51724623


Document: 

19-399

Date: 

September 1, 2020

Author(s):

Jun Wang and Yail J. Kim

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This paper presents the characteristics of a cost-effective ultra-high-performance concrete (UHPC) made of locally available constituents. The implications of steel and synthetic fibers on the shrinkage, maturity, and chloride permeability of the silica-based concrete are of interest. To implement assorted standard test methods, UHPC cylinders and prisms are cast and instrumented. The interaction between the fibers and cement paste affects the shrinkage of UHPC. Owing to the absence of coarse aggregate, the applicability of existing shrinkage models for ordinary concrete is not satisfactory; accordingly, a new expression is proposed. The early-age hydration of cement (less than 1 day) generates thermal energy, depending upon fiber type, which raises the temperature of the concrete. The load-carrying capacity of UHPC mixed with steel fibers is higher than that of UHPC with synthetic fibers. The maturity of UHPC is contingent upon fiber configuration; specifically, plain and steel-fiber-mixed UHPC cylinders show a superior early-age strength gain to those with synthetic fibers. For the Nurse-Saul and the Arrhenius maturity approaches (time temperature factor and equivalent age, respectively), regression equations are fitted. The flow of electric current and the resistivity of UHPC are favorable due to the densely formulated grain structure, leading to the improvement of durability when used for structural application. The diffusion coefficient of UHPC increases as the mixed fibers create interfacial gaps in the cement paste.

DOI:

10.14359/51725978


Document: 

19-320

Date: 

July 1, 2020

Author(s):

Bruce Menu, Thomas Jacob-Vaillancourt, Marc Jolin, and Benoit Bissonnette

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The experimental program reported in this paper sought to evaluate the efficiency of a range of curing methods in view of minimizing the evaporation rate at the surface of freshly placed shotcrete and preventing the detrimental consequences of early-age shrinkage. CSA A23.1-14 states that severe drying conditions should be considered to exist when the surface moisture evaporation rate exceeds 0.50 kg/m2/h (0.1 lb/ft2/h). In fact, the environmental conditions that lead to such evaporation rates are regularly experienced on construction sites, requiring that adequate protection of the concrete surface be carried out in a timely manner after placement. This research effort is aimed at quantifying the influence of selected curing methods upon the early-age moisture loss and the resulting shrinkage. The results show that early-age volume change of freshly sprayed shotcrete can be significantly reduced by adequate surface protection. Among the investigated methods, moist curing is found to be the most effective.

DOI:

10.14359/51724624


Document: 

19-324

Date: 

July 1, 2020

Author(s):

Dhanushika Gunatilake Mapa, Manjriker Gunaratne, Kyle A. Riding, and A. Zayed

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

Jointed plain concrete pavement (JPCP) repair slabs experience high incidences of early-age cracking due to high temperature rise and increased autogenous shrinkage of high-early-strength (HES) concrete mixtures. This paper presents an investigation to evaluate early-age cracking mitigation strategies of JPCP repair slabs. Finite element analyses were performed to understand the effects of physical phenomena leading to early-age cracking in JPCP repair slabs. While the analyses indicate the importance of concrete hydration kinetics and viscoelastic behavior on the early-age stress development in slabs, concrete moisture loss to the base was found to be the most significant phenomenon. Numerical modeling of concrete slabs was found to be useful in predicting the stress development in advance of costly field trials. Therefore, the proposed modeling approach can be applied to evaluate the performance of concrete mixtures prior to slab placement and thus improve and economize the current rigid pavement maintenance practices.

DOI:

10.14359/51725780


Document: 

18-512

Date: 

July 1, 2020

Author(s):

Mahdi Valipour and Kamal H. Khayat

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

DOI:

10.14359/51724613


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