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International Concrete Abstracts Portal

Showing 1-5 of 1355 Abstracts search results

Document: 

SP-349_35

Date: 

April 22, 2021

Author(s):

Alexandre Rodrigue, Josée Duchesne, Benoit Fournier and Benoit Bissonnette

Publication:

Symposium Papers

Volume:

349

Abstract:

Alkali-activated slag/fly ash concretes activated with combined sodium silicate and sodium hydroxide show good mechanical and durability properties in general. When tested in terms of resistance to freezing and thawing cycling in watersaturated conditions, the concretes tested in this study show final values of relative dynamic modulus averaging 100% after 300 cycles. However, all tested concretes showed poor performance towards freezing and thawing in presence of de-icing salts with only one tested mixture showing a final average scaling value below 0.5 kg/m². Early-age microcracking is observed on all tested concretes and is correlated to high values of autogenous shrinkage in equivalent paste mixtures. Increasing the fly ash content reduces both the observed autogenous shrinkage and early-age cracking. Low drying shrinkage values ranging from 470 to 530 μm/m after 448 days of measurements at 50% RH and 23°C are noted. The use of fly ash in these alkali-activated concretes reduces the expansion levels of concrete specimens incorporating alkali-silica reactive aggregates. With increasing fly ash contents (20, 30 and 40% replacement), decreasing expansions are observed for any given reactive aggregate. In general, the durability properties measured in this study were improved by partially substituting slag with fly ash as binder material.


Document: 

SP-349_20

Date: 

April 22, 2021

Author(s):

Klaus-Juergen Huenger, David Kurth, Maria Brigzinsky

Publication:

Symposium Papers

Volume:

349

Abstract:

Alumino-silicate compounds (geopolymers) are important for alternative binders for mortars and concretes. Such systems normally have a solid (metakaolin, slag, ash) and a liquid (activator solution) component. A newly developed system here consists of a waste silicate material and an aluminate source, both with a very good solubility. Under the addition of water only, a structure formation process occurs to form an alumino-silicate network. The Si/Al ratio can be varied in wide ranges to produce binders with different properties.

It was very surprising that the mortar properties not only depend on the recipe, but also on the aggregate types. Different aggregate types (quartz, greywacke, rhyolite, diabas, basalt, granodiorite) were chosen to produce mortar bars. All components were intensively mixed dry or as a slurry. Already the sand component affects the workability, further the setting time, the strength development and, of course, the durability. The best results were obtained with quartz, the worst with diabase or basalt sands. Obviously, the chemical and mineralogical composition and therefore the soluble constituents of the sand under highly alkaline conditions affected the structure formation process of the alumino-silicate binder and therefore the mortar properties too. The observed effects have nothing to do with an Alkali-silica-reaction (ASR).


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-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_01

Date: 

April 22, 2021

Author(s):

Carol Namnoum, Benoît Hilloulin,Maxime Robira, Frédéric Grondin, Ahmed Loukili

Publication:

Symposium Papers

Volume:

349

Abstract:

The production of cement by calcination of limestone releases large amounts of carbon dioxide. Development of concrete quality lead to optimize the sustainability and maintenance phases of concrete structures, so, using supplementary cementitious materials (SCM) is one of the methods adapted to reduce the environmental impact of cement production. In addition, self-healing of concrete appears as a process to considerably improve the durability of a damaged structure [1]. As revealed by most analyses, mineral additions can be used to improve the autogenous healing ability of cementitious materials [2].

In this study, the influence of using a combination of SCMs, such as ground granulated blast furnace slag and metakaolin, on the mechanism of autogenous crack healing was assessed in ternary formula. Self-healing evolution was characterised by means of mechanical tests carried out on notched mortar samples with different substitution ratios. The mechanical recovery was investigated after the healing period. Moreover, the micro-chemical structure of the healing products was determined using various techniques (TGA, SEM/EDS and XRD). The primary results showed that using metakaolin and ground granulated blast furnace slag together greatly improve the healing efficiency.


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