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Showing 1-10 of 295 Abstracts search results

Document: 

19-320

Date: 

July 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

4


Document: 

19-158

Date: 

July 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

4


Document: 

19-135

Date: 

July 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

4


Document: 

19-067

Date: 

March 1, 2020

Author(s):

Seyedhamed Sadati and Kamal H. Khayat

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

The research presented in this paper addresses the effect of coarse recycled concrete aggregate (RCA) on drying shrinkage of concrete designated for transportation infrastructure. Six types of RCA were employed at 30 to 100% replacement rates of virgin coarse aggregate. Two binder systems, including a binary cement with 25% Class C fly ash and a ternary system with 35% fly ash and 15% slag were employed. Three different water-cementitious materials ratios (w/cm) of 0.37, 0.40, and 0.45 were considered. Test results indicate that the use of RCA increased drying shrinkage by up to 110% and 60% after 7 and 90 days of drying, respectively. Correlations with R2 of up to 0.85 were established to determine the shrinkage at 7, 28, 56, and 90 days as a function of aggregate properties, including specific gravity, water absorption, and Los Angeles abrasion resistance of the combined coarse aggregates. The water absorption of the combined coarse aggregate was shown to be a good index to showcase the effect of RCA on shrinkage. Contour graphs were developed to determine the effect of RCA content and its key physical properties on 90-day drying shrinkage of concrete intended for rigid pavement construction. A classification system available in the literature was also used to suggest the maximum allowable replacement rates for use of RCA in a hypothetical case study. Results suggest replacement rates of 100%, 70%, and 50% (% wt.) to limit the 90-day shrinkage to 500 μɛ when RCA of A-1, A-2, and A-3 Classes are available, respectively.

DOI:

10.14359/51720296


Document: 

18-172

Date: 

March 1, 2020

Author(s):

Michael Dopko, Meysam Najimi, Behrouz Shafei, Xuhao Wang, Peter Taylor, and Brent Phares

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

This study investigated the effect of four volume dosages (that is, 0, 0.1, 0.3, and 0.5%) of high-elastic-modulus carbon microfiber, shrinkage-reducing admixture (SRA), and accelerating admixture (ACC) on the 24-hour compressive strength and restrained shrinkage of carbon microfiber-reinforced concrete. Additional 7- and 28-day compressive strength tests, as well as 1-, 7-, and 28-day splitting tensile strength tests, were carried out on the mixtures without and with 0.3% carbon microfiber. Results showed that, overall, increasing the carbon microfiber dosage increased the compressive strength, particularly at early ages. Splitting tensile strength results were used along with the restrained shrinkage ring results to quantify the restrained shrinkage cracking potential of the mixtures. It was found that carbon microfiber and SRA can both significantly reduce the drying shrinkage cracking potential of concrete. The combination of SRA and ACC in concrete provided compatible effects, characterized by increased early-age compressive strength, as well as reduced shrinkage and cracking potential.

DOI:

10.14359/51720297


Document: 

18-544

Date: 

March 1, 2020

Author(s):

Milena Rangelov, Somayeh Nassiri, Deviyani Gurung, and Timothy Ginn

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

Models are available to estimate the apparent moisture diffusivity (Da) of cement-based materials (CbMs) for internal relative humidity (h) prediction; however, these models include multiple nonunique shape parameters and are therefore impossible to manually calibrate. A common workaround is to use typical values, which are mostly outdated and inadequate for contemporary CbMs. This study presents an integrated procedure in which a finite difference inverse solution of Fick’s second law is linked with an advanced calibration software to identify and optimize the critical parameters of two widely used Da models. The observation dataset was h-profiles collected in mortar prisms from seven mixtures exposed to one-dimensional drying. Using the integrated method, the models’ parameters were optimized to fit the observation dataset. The impact of water-cement ratio and fly ash content on Da was established. Further, the critical parameters in both models were identified and correlated to different aspects of the pore system.

DOI:

10.14359/51722397


Document: 

19-035

Date: 

January 1, 2020

Author(s):

Aravind Tankasala and Anton K. Schindler

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

In this project, the effect of using lightweight aggregate (expanded slate) on the early-age cracking tendency of mass concrete mixtures was evaluated. Concretes representative of mass concrete mixtures—namely, normal-weight concrete, internally cured concrete, sand-lightweight concrete, and all-lightweight concrete—at two different water-cementitious materials ratios (0.38 and 0.45) were tested in cracking frames from the time of setting until the onset of cracking. The development of early-age concrete stresses caused by autogenous and thermal shrinkage effects were measured from setting to cracking. The behavior of concretes containing lightweight aggregates was compared with normal-weight concrete placed under temperature conditions simulating fall placement in mass concrete applications. Increasing the amount of pre-wetted lightweight aggregates in concrete results in systematic decrease in density, reduced modulus of elasticity, and reduced coefficient of thermal expansion. All these factors effectively improve the concrete’s early-age cracking resistance in mass concrete applications.

DOI:

10.14359/51719082


Document: 

19-017

Date: 

January 1, 2020

Author(s):

Ying-Hua Bai, Kang Shen, Sheng Yu, and Wei Chen

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

This paper studies the effects of VAE emulsion (vinyl acetate-ethylene emulsion, containing 70 to 95% vinyl acetate) on the setting time and mechanical properties of sodium metasilicate-activated slag-fly ash cementitious materials. Sodium metasilicate is used as an activator, and the alkali equivalent (mass percentage of Na2O provided by sodium metasilicate in the cementitious material) is 8%. The content of fixed fly ash, fine slag powder, and Na2SiO3 is 30, 54.26, and 15.74 wt.%, respectively. VAE emulsion is mixed with polymer-cement ratios (mass ratio of emulsion to cementitious material) of 2.5, 5, 7.5, and 10%. The water content in the emulsion is subtracted during the mixing and measuring. In the experiment, the emulsion and the activator are stirred well before they are mixed with the powder. Research shows that C-S-H gel is the main hydration product of sodium metasilicate-activated cementitious material and adding VAE emulsion does not produce new crystal hydration products. When the VAE emulsion content is higher than 5%, some unreacted polymer particles in the slurry exists, which can improve the toughness of the mortar and prolong the setting time of the cementitious material. However, the compressive strength of the mortar decreases and the dry shrinkage rate increases. The results of hydration heat and ion dissolution experiments show that with polymer coated on the surface of sodium metasilicate particles, the dissolution rate is reduced, and the hydration heat release of the cementitious material is slowed down. In addition, the dissolution rate and dissolution amount of sodium metasilicate are reduced, which increases the setting time of the cementitious material.

DOI:

10.14359/51719080


Document: 

18-563

Date: 

January 1, 2020

Author(s):

Hisham Qasrawi

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

Green self-consolidating concrete (SCC) is the aim of the construction industry nowadays. The accumulation of steel slag wastes causes severe environmental problems. These wastes can be recycled and replace natural aggregates, resulting in sustainable green SCC. In this research, natural aggregates in SCC are replaced, wholly or partly, by steel slag coarse aggregates (SSA) that were produced by crushing by-product boulders obtained from the steel industry. The fresh properties, (workability, stability, and bleeding), can all be attained when the suitable amount of SSA is used. SSA concrete increased the air content. Higher values are reported under hot conditions. The study shows that the 28-day compressive strength of SCC increased by approximately 10% when natural aggregate is replaced by SSA. However, adverse effects are reported when the ratio of SSA is more than 50%. Under hot weather, the strength was less and the optimum replacement ratio is 25%. The tensile strength of SCC increased by approximately 20% when natural aggregate is replaced by SSA. Adverse effects are reported when the ratio of SSA is more than 75%. Under hot weather, the same is observed but the value of the 28-day strength was lower. Special strength development mathematical relations are obtained and discussed. The modulus of elasticity increased by the increase in slag. The optimum value was at 50% for both conditions. An adverse effect is observed when the ratio of slag exceeds 75%. The drying shrinkage of concrete was lower for concrete containing SSA.

DOI:

10.14359/51719072


Document: 

18-542

Date: 

January 1, 2020

Author(s):

Jiarong Shen, Qianjun Xu, and Qingbin Li

Publication:

Materials Journal

Volume:

117

Issue:

1

Abstract:

The aim of this study is to quantitatively determine the effect of elevated temperatures on the pore structure and compressive strength of concrete. To minimize the effect of the hydration process, thermal and endogenous shrinkage, concrete cured in water for 12 months was tested. Evolutions of pore structure under elevated temperatures (40, 105, 150, 200, and 250°C [104, 221, 302, 392, and 482°F]) were characterized by mercury intrusion porosimetry (MIP), N2 adsorption, and scanning electron microscope (SEM) tests. Compressive strength tests were carried out to characterize the mechanical properties. The experimental results showed that with the increase of temperature, the porosity increased and the pore structure destroyed gradually. The changes in porosity and pore structure can be explained by the loss of water in concrete. In addition, the compressive strength decreased with increasing temperature. The relationship between compressive strength and porosity after heating at elevated temperatures fitted well with the strength-porosity logarithmic relation proposed by Schiller. The correlation coefficient is 0.994, which indicated that the effect of elevated temperature on the compressive strength of concrete can be quantitatively determined by Schiller function.

DOI:

10.14359/51718060


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