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International Concrete Abstracts Portal

Showing 1-5 of 588 Abstracts search results

Document: 

SP-349_49

Date: 

April 22, 2021

Author(s):

R.Douglas Hooton

Publication:

Symposium Papers

Volume:

349

Abstract:

Approximately 90% of the carbon footprint from concrete production is from portland cement (assuming portland cement is used as the sole cementitious binder). Therefore to reduce its carbon footprint, the amount of Portland cement clinker needs to be reduced. There are different ways of doing this, including optimization of combined aggregate gradations, use of water reducing admixtures, use of portland-limestone cements (PLC), and use of supplementary cementitious materials (SCMs). All of these measures can be taken simultaneously, but there is also concern that extreme measures (such as high SCM replacement levels) will reduce the robustness of concrete to abuse during construction, resulting in lower durability. Durability is important to obtain long service lives of concrete structures, and has a large impact on their carbon footprint.

This paper includes discussion of how each these measures if used prudently, can achieve significant reductions in carbon footprint while simultaneously improving durability in aggressive exposure conditions.


Document: 

SP-349_18

Date: 

April 22, 2021

Author(s):

Ivan Janotka, Michal Bačuvčík, Peter Paulík, and Lukáš Húlek

Publication:

Symposium Papers

Volume:

349

Abstract:

A layer of 2-4 mm (0.08-0.16 in) protective render coat (PRC) has proven to be an effective anticarbonation barrier at two bridges protecting the underlying concrete against carbonation for 100 years. The carbonation of concrete under the PRC with low permeability was found to be less than 2 mm (0.08 in). It is assumed that the PRC was placed for aesthetic purposes. Taking into account the considered XC3 exposure class according to EN 206, to which concrete structures were subjected and compressive strengths of the underlying concrete between 20 - 25 MPa (2900 - 3625 psi), low carbonation depth can be explained by the presence of the PRC applied on concrete surface. The main scientific goal of this article is to explain the cause of extremely low carbonation depth of concrete under the PRC. Its composition has been unknown until now but the present research reveals the secret of this substance. Investigations of the aspects of low carbonation depth thoroughly focused on the PRC role covering concrete beneath as well as material development of new current PRC based on the present cement and sand, without the use of chemical admixtures, are also the subject of ongoing research.


Document: 

SP-349_24

Date: 

April 22, 2021

Author(s):

Marta Roig-Flores, Eduardo J. Mezquida-Alcaraz, Ariel A. Bretón-Rodríguez, Juan Navarro-Gregori and Pedro Serna

Publication:

Symposium Papers

Volume:

349

Abstract:

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) is a type of concrete with superior mechanical and durability properties, which might be improved even further with the addition of nano-materials. This work studies the influence of adding nano-additions to two UHPFRCs with compressive strength around 150MPa (21755 psi), with and without crystalline admixtures. Two nano-materials were considered: cellulose nano-crystals (4-5 nm diameter, 50–500 nm length, 0.157-0.197 μin diameter, 1.97-19.7 μin length); in a dosage up to 0.15% by the cement weight; and aluminum oxide nanofibers (diameter 4-11nm, length 100-900nm, 0.157-0.433 μin diameter, 3.94-35.4 μin length) in a dosage of 0.25% by the cement weight. Water content of the mixes with nanomaterials was modified to maintain workability in a similar range aiming to maintain the self-compacting behavior. The following properties were analyzed: workability, compressive strength, modulus of elasticity and tensile properties calculated through a simplified inverse analysis after performing four-point bending tests. The study considered the effect of using three levels of mixing energy to ensure a proper dispersion of all the components, and its effect in the aforementioned properties. The results show a potential effect of these nanomaterials as nanoreinforcement, with slightly better ultimate strength and strain values for the higher energy level.


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-340-06

Date: 

April 1, 2020

Author(s):

Maria Kaszynska and Adam Zielinski

Publication:

Symposium Papers

Volume:

340

Abstract:

The research paper presents an analysis of autogenous shrinkage development in self-consolidating concrete (SCC). The first stage of the study involved an evaluation of concrete susceptibility to cracking caused by shrinkage of SCC with natural and lightweight aggregate. The shrinkage was tested on concrete rings according to ASTM C 1581/C 1581M- 09a. The influence of aggregate composition, the water content in lightweight aggregate, and SRA admixture on the reduction of concrete susceptibility to cracking, due to the early-age shrinkage deformation was determined. In the second stage of the research, the innovative method measurement of autogenous shrinkage was developed and implemented. The tests were performed on concrete block samples, dimensions 35x150x1150 mm, that had the same concrete volume as ring specimen in the ASTM method. Linear deformation of the concrete samples was measured in constant periods of 500 s using dial gauges with digital data loggers. The investigation allowed evaluating of the influence of water/cement (w/c) ratio of 0.28, 0.34, 0.42, and of aggregate composition on the development of autogenous shrinkage in different stages of curing SCC. The results were compared to existing material models proposed by other researchers. The conducted study indicated a significant influence of the w/c ratio and composition of aggregate on the concrete susceptibility to crack caused by the autogenous shrinkage deformation.


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