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International Concrete Abstracts Portal

Showing 1-5 of 236 Abstracts search results

Document: 

19-355

Date: 

September 1, 2020

Author(s):

Diogo Henrique de Bem and Ronaldo A. Medeiros-Junior

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

No widely accepted method is available to assess the efflorescence in small-scale mortar specimens. Thus, the analysis and determination of parameters that actually have an influence on the occurrence of efflorescence in cementitious materials become difficult to be accomplished, especially considering that its appearance in natural field conditions can take months or even years to happen. This paper has the objective to compare eight small-scale accelerated test methods for the assessment of efflorescence in lime-cement mortars and then to evaluate their sensibility to variations in the mixture composition. The results show that the method in which a water column introduces pressure produced the highest amount of efflorescence in the smallest time. The method was able to clearly identify the impact of silica fume towards the refinement of the porous microstructure and the efflorescence reduction. This study demonstrates that 28 days is enough time to finalize the accelerated testing proposed.

DOI:

110.14359/51724627


Document: 

19-347

Date: 

September 1, 2020

Author(s):

Yusheng Zeng, Ser Tong Quek, Aiping Tang, and Xianyu Zhou

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

Freezing-and-thawing (F-T) resistance is a key parameter in evaluating the durability of concrete. The response of concrete under F-T environment varies depending on the mixture proportion and materials used. This paper focuses on the F-T behavior and damage resistance of normal-strength (NC), high-strength (HSC), high-performance (HPC), and ultra-high-performance (UHPC) concrete. The mechanisms causing F-T damage are discussed, specifically based on expansion of freezable water under negative temperature and thermal stress arising from differences in the coefficient of thermal expansion of cement and aggregates. To quantify damage, two parameters—namely, mass loss ratio (MLR) and relative dynamic elastic modulus (RDEM)—are compiled for different classes of concrete. Results show that UHPC exhibited much lower increase in MLR and reduction in RDEM than NC and HPC, respectively. The effects of F-T loading on other mechanical properties of concrete such as compressive strength, flexural strength, tensile strength and stress-strain relationship are also investigated in this paper as possible parameters to help characterize F-T resistance. It is found that F-T will decrease the peak stress but increase the peak strain, and the flexural strength has the fastest loss rate for NC, HPC, HSC and UHPC, respectively. As concrete under F-T environment is often exposed to chloride, the significance of sodium chloride (NaCl) concentration and chloride diffusion coefficient (CDC) on HSC and UHPC under NaCl solution are studied. UHPC exhibits better resistance on chloride diffusion after F-T action due to denser internal pore structure. To improve the F-T resistance of concrete, the performance of two supplementary cementitious admixtures, fly ash and silica fume, to partially replace cement are studied. Results show that the appropriate fly ash replacement of 10 to 30% or silica fume replacement of 5 to 10% is found to enhance the F-T resistance. In addition, introducing fibers such as PVA or PP can improve the F-T resistance significantly, although using the wrong proportion may have a negative effect. Using combined admixture of polyvinyl alcohol and polyethylene fiber with 1.5% volume in cement-based composites reduces strength degradation caused by F-T loadings.

DOI:

10.14359/51725781


Document: 

18-403

Date: 

July 1, 2020

Author(s):

S. Lavanya Prabha, M. Gopalakrishnan, and M. Neelamegam

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

This investigation was carried out to develop high-strength cementitious composite mixtures of compressive strength greater than 90 MPa (13.05 ksi). The main aim of this study is to develop high-strength cementitious composites having high density with low void content. To achieve the requirement, cement, copper slag, quartz powder, and silica fume ingredient proportions were arrived by optimum partial packing as well as the Dewar and Larrard method. More than 60 cementitious composite mixtures with and without high-strength micro-steel fiber and chopped basalt fiber were prepared and their compressive strength at the age of 28 days cured under normal water curing was investigated. In all the investigated trial mixtures, 100% copper slag was used instead of normal river sand and a required quantity of high-range water-reducing admixture (HRWRA) was used to maintain workability. Based on the 28-day compressive strength (greater than 90 MPa [13.05 ksi]), four cementitious composite mixtures were selected as optimized mixtures and their mechanical and durability properties were evaluated as per Indian Standard IS 516 and ASTM C469, and their rapid chloride permeability was assessed by ASTM C1202. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis were also carried out on four optimized composite mixtures. This project aims to develop mixtures suitable for the construction of storage buildings for arms and ammunition of defense research and development organizations (DRDO), and also these composites can be used in many special applications where high mechanical and durability properties are required.

DOI:

10.14359/51725778


Document: 

19-328

Date: 

July 1, 2020

Author(s):

Jedadiah F. Burroughs, Charles A. Weiss Jr., John E. Haddock, and W. Jason Weiss

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

This study presents the application of an analytical model to describe the rheological behavior of cement pastes containing silica fume at replacement rates of up to 30% by mass. The analytical model hypothesizes how water interacts with particles in a cementitious system. The coating thickness of water surrounding each particle in the system is estimated. This coating thickness is shown to correlate strongly with measured rheological properties when fit to the Herschel-Bulkley model. To calculate coating thickness, it is necessary to account for the water absorbed by nonhydraulic components in the system, whether aggregate, supplementary cementitious materials, or mineral. The results suggest that silica fume particles may be absorptive, and this absorption capacity, although small, must be considered when designing water-starved cementitious materials. The experimental investigation involved the rheological testing of three water-binder ratios (0.20, 0.30, 0.45), three silica fume replacement levels (10%, 20%, 30%), and eight different silica fume products.

DOI:

10.14359/51724626


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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