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International Concrete Abstracts Portal

Showing 1-5 of 111 Abstracts search results

Document: 

SP-349_52

Date: 

April 22, 2021

Author(s):

Thibaut Marchi, Marie Salgues, Eric Garcia Diaz, Jean Claude Souche, and Philippe Devillers

Publication:

Symposium Papers

Volume:

349

Abstract:

Recent studies focused on the quality of the interfacial transition zone (ITZ) of ordinary concretes made from recycled aggregates (RA), without however focusing on High Performance Concretes (HPC).

This paper aims to formulate HPC from RA that are exclusively derived from concrete, whose composition is controlled. These concretes are made in a ready-mixed concrete plant and then undergo a crushing and riddling process to produce RA. Partially saturated gravels are substituted up to 100% in the HPC composition in order to accentuate internal cure phenomenon. This phenomenon was observed and demonstrated using a scanning electron microscope (SEM) in the low Water/Cement (W/C) paste up to a distance of 150 μm from the RA and compared by image processing, to a reference concrete made from natural aggregates (NA).

The comparison of the mechanical performances and the microscopic analysis of HPC show that the characteristics transfer of the RA seem to favor a hydration of the paste by a mechanism of desorption of their absorbed water, in a process of “internal cure”. The internal cure appears optimal for concrete C60. In addition to this observation, there was an increase in the strength of the recycled HPCs compared to control natural-aggregate HPCs.


Document: 

SP-349_30

Date: 

April 22, 2021

Author(s):

Faisal.A.H Saleh, Nouria Kaid, Kada Ayed, Rabah Soltani, And Djamel-Eddine Kerdal

Publication:

Symposium Papers

Volume:

349

Abstract:

Scrap tyres are one of the most serious wastes that are landfilled with small percentages. Recycled scrap tyres are being used in different domains of industry because they are notdegradable. The experimental work focused on mechanical properties and durability indicators of self-compacting sand concretes blended with recycled rubber. Such modified concretes comprised 5, 10, 15 and 20% of rubber fine powder (RFP) and coarse particles (RCP) as partial substitutions of natural sand and aggregates. To shed light on physical and mechanical properties rubber particles effects, ordinary vibrated and self-compacting as well as self-compacting sand concretes (SCSCs) were characterised. Special attention was given to compression and bending performances of SCSCs. Identification of two durability indicators — water porosity and density — was assessed, according to AFGC specifications. Experimental findings enhanced previous literature reported statements and demonstrated that use of rubber particles as substitutes improved performances of elaborated SCSCs and produced eco-friendly materials that are appropriate for large surface applications such as pavements and terraces as well as civil engineering constructions.


Document: 

SP-349_15

Date: 

April 22, 2021

Author(s):

Jamal Medljy, Hilal El-Hassan, and Tamer El-Maaddawy

Publication:

Symposium Papers

Volume:

349

Abstract:

This paper focuses on developing ambient-cured alkali-activated concrete incorporating recycled concrete aggregates (RA). The binder was either slag or a blend of slag and fly ash (3:1, by mass). Hook-ended steel fibers were added, in 2% volumetric fraction, to improve the properties of concrete made with RA. The alkaline activator solution was a blend of sodium silicate and sodium hydroxide. Concrete mixtures were proportioned to achieve three target compressive strengths, namely 30, 45, and 60 MPa. The performance of concrete mixtures was assessed based on 1, 7, and 28-day compressive strengths. Experimental results showed that full replacement of natural aggregates by RA caused up to 28% reduction in compressive strength of plain alkali-activated slag concretes, with greater reductions being reported in mixtures with higher target strength and tested at 28 days. The incorporation of 2% steel fibers enhanced the strength and caused limited strength reductions of up to 7%. Compared to alkali-activated slag RA concretes, mixtures with 25% fly ash replacement exhibited lower strengths at 1 and 7 days, but their 28-day strength was superior. Analytical multi-linear regression models were developed to identify statistical significance of concrete components and examine their impact on the compressive strength.


Document: 

SP-349_51

Date: 

April 22, 2021

Author(s):

Erandi Ariyachandra, Sulapha Peethamparan

Publication:

Symposium Papers

Volume:

349

Abstract:

The utilization of recycled concrete as an adsorbent to sequester NO2 without additives or catalysts is an innovative, cost-effective, and sustainable approach to capture NO2 from targeted industrial facilities. During NO2 sequestration, alkaline products such as calcium hydroxide (CH) in the adhered old mortar of recycled concrete can react with NO2 to form Ca(NO2)2 and Ca(NO3)2. Thus, the use of NO2 sequestered recycled concrete aggregates (NRCA) as a constituent of concrete can be beneficial since Ca(NO2)2 and Ca(NO3)2-based chemical compounds are widely used as multi-functional admixtures for concrete applications. This study investigates the influence of the properties of the parent (demolished) concrete on the mechanical and durability performance of NRCA incorporated ordinary portland cement (OPC) concrete. Two types of recycled concrete aggregate (RCA) were derived from 2 and 20-year old concrete blocks to produce two types of NRCA—2-NRCA (2-year-old NRCA) and 20-NRCA (20-yearold NRCA) by exposing them to a humidified air/NO2 mixture (at RH = 50% and 23±2°C) for two weeks. NRCA was used as a partial replacement for natural fine aggregate in fresh OPC mixtures at 20% and 40% rates by volume. The influence of NRCA on concrete compressive strength, porosity, and long-term chloride diffusion coefficients were assessed. In addition, open-circuit and potentiodynamic polarization tests were conducted to evaluate the resistance to chloride-induced corrosion of steel in concrete. Control test mixtures containing a commercially available Ca(NO2)2 based corrosion inhibitorwere also tested for comparison purposes. Both types of NRCA enhanced the mechanical and durability properties of concrete compared to control mixtures. Test mixtures containing 2-NRCA showed better resistance against chloride-induced corrosion than concrete with 20-NRCA.


Document: 

SP-347_10

Date: 

March 1, 2021

Author(s):

Grace Darling, Stephan A. Durham, and Mi G. Chorzepa

Publication:

Symposium Papers

Volume:

347

Abstract:

Concrete median barriers (CMB) are installed to decrease the overall severity of traffic accidents by producing higher vehicle decelerations. In 2016, an update to the AASHTO Manual for Assessing Safety Hardware (MASH) saw a 58% increase in impact severity of test level 4 (TL-4) impact conditions when compared to the NCHRP Report 350 testing criteria. This study investigates the use of fiber-reinforced rubberized CMBs in dissipating the impact energy to improve driver safety involved in crashed vehicles. Two full-scale barrier prototypes with shear keys were constructed and tested under impact conditions in a laboratory setting. Compared to the Georgia Department of Transportation specified single-slope barrier, the fiber-reinforced rubberized concrete mixture, a design with 20% replacement of the coarse aggregate by volume with recycled rubber tire chips and a 1.0% steel fiber addition, was evaluated based on its performance in toughness, energy absorption capacity, and its recoverable deformation. It is concluded that the TC20ST1 barrier performed as well as the control barrier at the impact load of 150.0 kips (667.2 kN), with neither barrier experiencing any visible damage.


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