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International Concrete Abstracts Portal

Showing 1-5 of 177 Abstracts search results

Document: 

19-051

Date: 

November 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

6


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: 

19-281

Date: 

July 1, 2020

Author(s):

Nader Ghafoori, Iani Batilov, and Meysam Najimi

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The objective of this study was to evaluate the effectiveness of colloidal nanosilica (nS) as a nanomaterial and pozzolanic admixture to mitigate the deteriorative effects of sodium sulfate-based physical salt attack (PSA) on portland cement mortars. Mortar mixtures of an ASTM C150 Type II (<8% C3A) or a Type V (<5% C3A) portland cement were prepared with 0, 3, and 6% cement replacements with either nS or microsilica (mS). Test samples were subjected to 3 years of exposure under a constant or cyclic PSA-conducive environment. The PSA results were supported with additional water absorption, rapid sulfate ion permeability (RSPT), and porosimetry testing. The Type V cement mortars containing nS exhibited the most observable scaling and flaking under both conditions of PSA exposure. The addition and increase in cement replacement with nS had a clear detrimental effect to PSA resistance for both cement types and both types of PSA exposure. Results indicated nS reduces permeability and diffusion in mixtures of either cement type which, for PSA, the denser and more refined pore network proved conducive to higher damaging tensile stresses and distress. The larger the measured volume of permeable pore space through absorption, the less susceptible the mortars were to PSA, which is counterproductive to conventional good practice of designing high-durability concrete via reducing permeability and sorption, and increasing a mixture’s watertightness.

DOI:

10.14359/51725779


Document: 

19-205

Date: 

May 1, 2020

Author(s):

Rabab Allouzi, Aya Al Qatawna, and Toqa Al-Kasasbeh

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Foamed concrete is currently studied to investigate its feasibility to be used structurally to produce a lightweight concrete mixture that is workable and has sufficient mechanical properties. This encouraged this research to design a foamed concrete mixture to be used in the construction industry. The main parameters that shall be satisfied for structural use are the workability, density less than 1900 kg/m3, and minimum cylinder compressive strength of 17 MPa (2500 ksi) based on ACI 213R. In this paper, 14 different foamed concrete mixtures are designed and tested to investigate their applicability. As fly ash quality affects foamed concrete permeability and as foamed concrete has low resistance to concentrated stresses, the proposed mixtures do not contain fly ash and are reinforced with polypropylene (PP) fibers. The effect of water-cement ratio (w/c), sand-cement ratio (s/c), PP fibers content, and the foam agent content are investigated. It is found that the compressive strength increases with the increase in density. The optimum s/c is 1:1, w/c is 0.4, and the PP fibers content is 1% by weight of cement. A relationship of splitting tensile strength relative to compressive strength is proposed.

DOI:

10.14359/51722405


Document: 

19-181

Date: 

March 1, 2020

Author(s):

Robert E. Melchers and Igor A. Chaves

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

This paper deals with long-term corrosion of steel reinforcement and how that is influenced by the presence of chlorides in the concrete. It provides experimental evidence that so-called “chloride-induced” long-term corrosion is the result of the accelerating effect of chlorides on the dissolution and loss of calcium hydroxide from concretes. This process progressively moves into the concrete, lowers its pH, increases its permeability, and facilitates inward diffusion of atmospheric oxygen. When these conditions reach the reinforcement, a high rate of reinforcement corrosion becomes thermodynamically possible and is observed in the experiments. It occurs earlier for concrete matrixes more open in structure. This can be attributed to greater internal surface area of exposed calcium hydroxide. The results also show that elevated concentrations of chlorides alone are not sufficient for causing long-term corrosion. The presented results throw a new light on chloride-induced corrosion under long-term exposures.

DOI:

10.14359/51722400


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