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International Concrete Abstracts Portal

Showing 1-5 of 151 Abstracts search results

Document: 

SP-349_37

Date: 

April 22, 2021

Author(s):

O. Ahmadah, H. Bessaies-Bey, A. Yahia, and N. Roussel

Publication:

Symposium Papers

Volume:

349

Abstract:

Low environmental impact binders, in which clinker is partially substituted by less reactive powders, are used in proportioning low water-to-cement ratios mixtures to ensure higher compactness, low porosity and improved mechanical as well as durability properties. The use of relatively high solid volume fractions dramatically affects the workability of the mixture and affects its ease of placement and consolidation. Various superplasticizer types have been investigated in literature to control the rheological properties, although these admixtures considerably decrease the yield stress values, their effect on viscosity is moderate. The main objective of this investigation is to control the rheology of ternary cements by controlling the morphology of particles, which is the key parameter affecting the rheology of cementitious suspension. The test results on LC3 (i.e. 55% Portland cement + 30% calcine clay + 15% Limestone) and CEM II/B-M (S-LL) (i.e. 65% Portland cement + 20% Slag + 15% Limestone) ternary binders revealed that the optimization of the particlesize distribution and the maximum packing fraction of the powders leads to a considerable decrease of both viscosity and yield stress by 20% and 50%, respectively.


Document: 

SP-349_13

Date: 

April 22, 2021

Author(s):

Gonzalo A. Lozano Rengifo, Mayra T. de Grazia, Leandro F. M. Sanchez, and Edward G. Sherwood

Publication:

Symposium Papers

Volume:

349

Abstract:

Reducing Normal Portland Cement (NPC) has been a major concern of concrete industry and research community over the last 2-3 decades. As much as 8% of the global CO2 emissions stem from clinker production. Hence, a wide number of research projects have been focusing on reducing NPC in cementitious materials using numerous strategies such as the use of supplementary cementing materials (SMC’s), limestone fillers (LF) and/or advanced mixproportioning techniques. Yet, the impact of these procedures on the overall behaviour of materials with low NPC content, especially in the fresh state and long-term durability, is still not fully understood. This work aims to understand the influence of the distance between the fine particles, the so-called Inter-Particle Separation (IPS), on the fresh state behaviour of cement-base pastes designed through the use of Particle Packing Models and incorporating LF. Evaluations on the fresh (i.e. rheological behaviour and setting time) and hardened states (compressive strength) were conducted in all mixtures. Results show that IPS directly correlates with the viscosity of cementbase pastes for all shear rates appraised. Moreover, the use of LF increases the hydration rate of NPC pastes. Finally, it is clear that the water-to-cement ratio keeps being the main factor controlling the compressive strength of cement pastes with reduced NPC content and high levels of LF replacement.


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: 

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: 

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.


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