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International Concrete Abstracts Portal

Showing 1-5 of 140 Abstracts search results

Document: 

SP326-05

Date: 

August 10, 2018

Author(s):

Ravindra Gettu, Radhakrishna G. Pillai, Jyotiprakash Meena, Anusha S. Basavaraj, Manu Santhanam, and B.S. Dhanya

Publication:

Symposium Papers

Volume:

326

Abstract:

The mixture proportioning of concrete for sustainability should consider four aspects, without sacrificing affordability: the lowering of the carbon dioxide emissions; the minimization of raw materials required; reduction of energy demand during manufacturing and construction; and the longevity of the structure or other applications. Taking a set of concretes with different binders, including ordinary portland cement (OPC), fly ash (FA) and ground granulated blast furnace slag (GGBS), sustainability is assessed using different types of indicators including those that take into account the binder and clinker content, compressive strength, carbon footprint and energy demand. A new set of indicators called A-indices has been proposed for combining the influence of carbon dioxide emissions obtained from life cycle assessment (LCA) and durability parameter that relate to the service life of a structure. Here, this concept is illustrated by obtaining a parameter based on the chloride migration coefficient of the concrete. It is proposed that the decision-making process for sustainable concrete be made by minimizing both the A-index and the energy intensity, defined as the energy demand for a unit volume of concrete and unit performance parameter, such as 1 MPa of 1-year compressive strength. The best concretes considered here come out as those with ternary binders having 40% of the OPC replaced by a combination of GGBS and FA.


Document: 

SP326-40

Date: 

August 10, 2018

Author(s):

A. Ghani Razaqpur and Gholamreza Fathifazl

Publication:

Symposium Papers

Volume:

326

Abstract:

Macro-mechanics is a rational basis for determining some of the mechanical properties of concrete based on its composition. In this investigation, well known macro-mechanical models for elastic modulus of Natural Aggregate Concrete (NAC) are adapted and generalized to make them applicable to Recycled Aggregate Concrete (RAC). Two sets of models are presented: (1) Phase-Based Models: where the elastic modulus is expressed in terms of the volume fractions and elastic moduli of relevant concrete mixture constituents, (2) Bulk-Based Models: where the elastic modulus is expressed in terms of the total mortar and aggregate volumes and elastic moduli of two limiting mixes, one with 0% and the other with 100% replacement of coarse natural aggregate by RCA. The detailed procedures are presented and the derived expressions for evaluating the elastic modulus are shown. To validate the proposed models, results of an experimental program involving many NAC and RAC mixes are used, with the mixes proportioned by either the traditional method of the American Concrete Institute (ACI) or by the Equivalent Mortar Volume (EMV) method developed by the writers. Reasonable agreement is observed between the computed and corresponding experimentally measured elastic moduli, with maximum difference of 12%.


Document: 

SP314-05

Date: 

March 1, 2017

Author(s):

Michael Berry, Bethany Kappes, and David Schroeder

Publication:

Symposium Papers

Volume:

314

Abstract:

This paper documents research focused on evaluating the feasibility of using minimally processed reclaimed asphalt pavement (RAP) as aggregate replacement in concrete pavements. A statistical experimental design procedure (response surface methodology – RSM) was used to investigate proportioning RAP concrete mixtures to achieve desired performance criteria. Based on the results of the RSM investigation, two concrete mixtures were selected for further evaluation: a high RAP mix with fine and coarse aggregate replacement rates (by volume) of 50 and 100 percent respectively, and a “high” strength mix with one half of the RAP used in the high RAP mix. These two concrete mixtures were subjected to a suite of mechanical and durability tests, and were used in a field demonstration project to evaluate their potential use in pavements. Mechanical properties tested were compressive and tensile strength, elastic modulus, shrinkage, and creep. Durability tests included alkali-silica reactivity, absorption, abrasion, chloride permeability, freeze-thaw resistance, and scaling. Overall, both mixes performed adequately in these mechanical and durability tests, although the inclusion of RAP negatively impacted most of the tested properties relative to those of control mixes made with 100 percent conventional aggregates.


Document: 

SP314-09

Date: 

March 1, 2017

Author(s):

Ardavan Yazdanbakhsh, Lawrence C. Bank, and Jonathan Rosen

Publication:

Symposium Papers

Volume:

314

Abstract:

In the past, many investigations have studied the effect of replacing coarse natural aggregate (CNA) with coarse recycled concrete aggregates (CRCA) on “material” properties of concrete, particularly compressive strength. This article reports on a research program in which (1) commonly used and practical methods were used for mixture design, proportioning, and production of CRCA and CNA concrete batches, (2) reinforced concrete beam specimens were produced from both types of concrete and tested in a bending configuration for measuring load-deflection response, moment capacity, and failure mode, and (3) a theoretical investigation was performed to predict the effect of concrete strength on the moment capacity of the beams. The test results showed, as predicted by the theoretical study, that the reduction in moment capacity caused by the strength loss due to the replacement of natural aggregate with CRCA, was negligible. It was also observed that the scatter of load carrying capacities of CRCA and CNA concretes were both very low and had coefficient of variation values of 0.048 and 0.064 respectively.


Document: 

SP305-43

Date: 

September 1, 2015

Author(s):

Tarun R. Naik; Fethullah Canpolat and Giacomo Moriconi

Publication:

Symposium Papers

Volume:

305

Abstract:

Concrete durability-related properties are known to be negatively affected due to expansion and cracking that result from factors such as freezing and thawing actions, alkali-aggregate reactions, sulfate attack, corrosion of the reinforcement, shrinkage, and other similar factors. Durability, and, therefore, sustainability of properly designed and constructed concrete structures depends primarily upon the quality of the materials of construction and other simple, but critical, steps. Concrete construction can last 100 years or more if five simple "steps" are followed: (1) materials selection; (2) structure design; (3) construction; (4) quality management; and, (5) timely evaluation, maintenance, and repairs. This is a holistic approach. Most mistakes are made in not satisfactorily following Steps 4 and 5. Conventional mixture proportioning technique used for production of high-strength concrete does not guarantee long-term durability of concrete. Concrete mixtures must be proportioned to attain desired workability, high-dimensional stability, high-strength, and high-durability related properties; i.e., high-quality concrete (HQC). However, mixture proportioning requirements for HQC must be varied according to the type and expected use of the concrete construction. HQC mixtures must have high-quality constituent materials: durable aggregates, low heat of hydration cement, mineral additives, and chemical admixtures. Furthermore, the mixing water must be minimized (i.e. a low water to cementitious materials ration, W/Cm). A strict quality control is also needed in various aspects of the production of HQC. Research activities conducted at the UWM Center for By-Products Utilization (UWM-CBU), CANMET, and elsewhere, have demonstrated that HQC mixtures can be proportioned to obtain strength in excess of 100 MPa (14,000 psi) and service life of 100 plus years.


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