International Concrete Abstracts Portal

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International Concrete Abstracts Portal

Showing 1-9 of 9 Abstracts search results

Document: 

SP294-08

Date: 

October 4, 2013

Author(s):

Jussara Tanesi, Dale Bentz, and Ahmad Ardani

Publication:

Special Publication

Volume:

294

Abstract:

One of the primary approaches to producing more sustainable concretes consists of replacing 50 % or more of the portland cement in a conventional concrete with fly ash, producing a so-called high volume fly ash (HVFA) concrete. While these mixtures typically perform admirably in the long term, they sometimes suffer from early-age performance issues including binder/admixture incompatibilities, delayed setting times, low early-age strengths, and a heightened sensitivity to curing conditions. Recent investigations have indicated that the replacement of a portion of the fly ash in these concrete mixtures by a suitably fine limestone powder can mitigate these early-age problems. The current study investigates the production of concrete mixtures where either 40 % or 60 % of the portland cement is replaced by fly ash (Class C or Class F) and limestone powder, on a volumetric basis. The mixtures are characterized based on measurement of their fresh properties, heat release, setting times, strength development, rapid chloride penetrability metrics and surface resistivity. The limestone powder not only accelerates the early age reactions of the cement and fly ash, but also provides significant benefits at ages of 28 d and beyond for both mechanical and transport properties.

10.14359/51686325


Document: 

SP294-07

Date: 

October 4, 2013

Author(s):

Lapyote Prasittisopin and David Trejo

Publication:

Special Publication

Volume:

294

Abstract:

Rice husk ash can be used as a supplementary cementing material. It is a waste material from the burning of rice husks for energy. Rice husk ash contains a mesoporous morphology of silica and this morphology has high hydrophilic properties. When rice husk ash is used in concrete mixtures, the flowability of the mixtures decreases. This makes the acceptance of rice husk ash in the concrete industry more challenging. Reduced workability hinders the potential use of rice husk ash in the field. Some research has investigated the potential use of using mechanical grinding (e.g., ball mill) to reduce particle size of rice husk ash with the hopes of improving the workability of concrete containing RHA, but this method requires significant energy and results in high wear of the equipment. The work investigates the use of a chemical treatment process of rice husk ash. This chemical treatment process reduces the particle size and breaks down the mesoporous morphology, thereby improving the fresh characteristics of concrete containing RHA and decreasing its water requirements. Because changes in setting behavior and reduced early-age strength development are other concerns when using some supplementary cementing materials, this work also investigates the setting, early-age compressive strength development, and porosity of cementing material systems containing 10% and 15% RHA replacements.

10.14359/51686324


Document: 

SP294-06

Date: 

October 4, 2013

Author(s):

Raj Patel and Fred Kinney

Publication:

Special Publication

Volume:

294

Abstract:

The fly ash based hydraulic binder (FAHB) described in this paper is comprised of ASTM Class C fly ash, ASTM class F fly ash and two proprietary non-caustic liquid activators. FAHB, a zero carbon footprint binder, is successfully used in making Green Concrete (eGC.) The eGC neither needs wet curing like Portland cement Concrete (PCC) nor needs elevated curing temperature like geopolymer cement concrete. The water demand of eGC is much lower than the water demand of PCC. Though, eGC follows Abrahms’ water-to-cement ratio (W/C) law, it has different sets of curves to estimate the W/C from the required 28-day compressive strength of concrete (f’cr). A little different approach is needed for proportioning the eGC using FAHB. This paper presents the model for estimating the water demand of eGC, the approximate relation between the W/C and f’cr and the step- by- step guideline for mix proportioning of eGC using FAHB, a carbon neutral binder system consisting of no Portlannd cement. The mixture proportioning method proposed in this paper will help concrete engineers and ready mixed concrete producers in designing cost effective and durable eGC. This method permits users to design eGC for wide range of workability and compressive strength.

10.14359/51686323


Document: 

SP294-05

Date: 

October 4, 2013

Author(s):

Samson T. Tassew and Adam S. Lubell

Publication:

Special Publication

Volume:

294

Abstract:

Compared to the hydration process of traditional Portland cements, phosphate-based cements rely on an acid/base reaction process to quickly achieve strong, lightweight and durable binders with lower embodied energy. Since the binding action relies on the chemical composition of the initial components, the rheological and mechanical properties of the resulting ceramic concretes can also be influenced by other mix components including fly ash, fillers and aggregates. This paper reports on an ongoing study examining properties of concretes produced with magnesium potassium phosphate cement binders that incorporate fly ash contents of up to 80% of the total binder mass. Highly flowable mixes were developed with setting times that could be controlled through use of commonly available admixtures. The highest compressive strength of the binders and mortars were achieved when the fly ash content was 50% of the total binder mass. The produced binders and sand mortars had densities of 1800 kg/m3 [3034 lb/yd3] and 2100 kg/m3 [3540 lb/yd3] and compressive strengths of 35 MPa [5.0 ksi] and 60 MPa [8.7 ksi] after 28 days of simple ambient curing. Decreases in both strength and density were observed as the fly ash content was increased further, but remained within practical ranges for common construction applications with high fly ash contents.

10.14359/51686322


Document: 

SP294-04

Date: 

October 4, 2013

Author(s):

E. Ivan Diaz Loya, Fred Kinney and Carlos Augusto Orozco Rios

Publication:

Special Publication

Volume:

294

Abstract:

Over the last few decades there has been an increasing interest in low-carbon-foot-print binders that can replace hydraulic cement in concrete mixtures. Given that hydraulic cement is so ingrained in the building materials industry, alternative binders –in addition to offering a low carbon footprint– must exhibit similar or improved consistency and properties in a cost effective manner. A candidate that meets these criteria is activated high-calcium fly ash (AHCFA), which as the name implies uses high-calcium fly ash (HCFA) as main reactive powder along with an activator to increase its hydraulic activity and a setting retarder to regulate the rate of reaction. It is an attempt to get a better understanding of the factors that have greater influence in the reactivity of HCFA. The physical, chemical and crystallographic characterization as well as glass fragility analyses of several HCFA samples was paralleled with the compressive strength of their corresponding AHCFA mortars. Correlations between HCFA characteristics and the compressive strength of the resulting AHCFA mortars were sought. The results suggest that the reactivity of HCFA can be evaluated in terms of glass fragility using non-bridging oxygens per tetrahedron (NBO/T) and alumina saturation index (ASI) as main parameters.

10.14359/51686321


Document: 

SP294-03

Date: 

October 4, 2013

Author(s):

Mary U. Christiansen and Lawrence L. Sutter

Publication:

Special Publication

Volume:

294

Abstract:

Waste glass is considered for use in a geopolymer binder systems based on the high Si content, amorphous framework structure, adequate hardness and widespread availability. A lack of Al within the system, however, must be taken into account, as Si/Al and Na/Al ratios have been shown to affect properties such as setting time, compressive strength and microstructure. Metakaolin and fly ash were added to a glass-based system, lowering the Si/Al and bringing Na/Al closer to unity. Mortars made using 100% glass as well as 25 and 50% of fly ash or metakaolin by mass were activated with 10M NaOH and cured at 80°C for 24 hours. Microstructural characterization of fracture surfaces and thin sections as well as compressive strength and degree of reaction data was collected. The 100% glass mixture (Si/Al – 8.39, Na/Al – 1.61) and 25% metakaolin (Si/Al – 4.96, Na/Al – 0.97) mixtures showed a dense, continuous microstructure. The 25% MK mix resulted in a 1-day f’c of above 5000 psi (35 MPa), while the 50% metakaolin mixture (Si/Al = 3.45, Na/Al – 0.69) developed little strength and had a low-density microstructure, possibly due to the high water demand. Mixtures containing fly ash resulted in reasonable compressive strengths and moderately dense microstructures.

10.14359/51686320


Document: 

SP294-02

Date: 

October 4, 2013

Author(s):

Katherine L. Aughenbaugh, Paul Stutzman and Maria C. G. Juenger

Publication:

Special Publication

Volume:

294

Abstract:

Geopolymers are made from natural or waste aluminosilicate powders that come from a variety of sources and have highly variable compositions. These powders are mixed with caustic solutions, which must be selected carefully to optimize strength and durability. Geopolymer cement can be designed by tailoring caustic solution composition to the reactive phase composition of the solid component of the mixture; however, assessing which phases are reactive is challenging for complex and heterogeneous solids such as fly ash. Previous research has suggested that scanning electron microscopy and multispectral image analysis (SEM‐MSIA) can be used to identify and quantify the glassy phases in fly ash and allows for the determination of how these phases dissolve over time in caustic solutions. In this study, a Class F fly ash was analyzed for phase content using x‐ray diffraction and Rietveld analysis (RQXRD) and SEM‐MSIA, which identified multiple glassy phases in the fly ash. Next, the fly ash was suspended in 8 M NaOH and tested at various time intervals with SEM‐MSIA to track changes in the amounts of each individual glassy phase initially identified in the fly ash. The results showed that for this fly ash, all of the glassy phases identified were reactive in the alkaline solution and decreased in amount after being subjected to the sodium hydroxide solution. Two distinct reaction products were identified for this fly ash as well.

10.14359/51686319


Document: 

SP294-01

Date: 

October 4, 2013

Author(s):

Shiho Kawashima, Pengkun Hou, Kejin Wang, David J. Corr, and Surendra P. Shah

Publication:

Special Publication

Volume:

294

Abstract:

Due to the high carbon emissions that result from cement production, it is desirable to limit the cement content of concrete to make it a more sustainable material. This is possible through substantial replacement of cement with supplementary materials, such as fly ash. The positive effects of this approach are twofold. First, reducing the cement content of concrete will reduce its carbon footprint. Second, fly ash is a coal combustion by-product, so essentially a waste material, which must be stored in landfills and enclosures if unused. Therefore, the productive use of fly ash by incorporating it into building materials at high volumes can help alleviate a waste storage issue. This paper is a summary of studies performed at the Center for Advanced Cement-Based Materials - Northwestern University, in collaboration with Iowa State University, relating to the activation of fly ash through nanomodification. Through seeding effects and increased reactivity, nanoparticles can accelerate cement hydration and subsequently the production of calcium hydroxide (CH), which can help activate the pozzolanic reaction of fly ash particles. Two types of nanoparticles are discussed in this summary paper: silica (SiO2) and calcium carbonate (CaCO3). The study on CaCO3 nanoparticles addresses the issue of dispersion, which is critical for nanomaterials, and the resultant effects on the hardening and early-age properties of fly ash-cement pastes. And the study on nano SiO2 focuses on determining the mechanisms underlying the effect of the pozzolanic nanoparticle on the early-age and long-term compressive strength gain of fly ash-cement mortars.

10.14359/51686318


Document: 

SP294

Date: 

October 4, 2013

Author(s):

Editors: Narayanan Neithalath and James Hicks / Sponsored by ACI Committees 130, 232, and 236

Publication:

Special Publication

Volume:

294

Abstract:

There is a growing interest all over the world to develop and implement environmentally friendly binding materials for concrete applications. The emphasis of the research and construction community is on finding sustainable alternatives for ordinary portland cement to reduce the overall environmental and energetic impact of cement production. The use of high volumes of fly ash and slag are already accepted means of cement reduction for sustainable concretes; however, the dramatic increase in the consumption of concrete requires novel and sustainable binder systems. Recent research results is to provide an introduction into several areas of active work on green binder systems. The papers in this CD deal with a wide variety of topics that are of significant interest and impact, including the chemistry of geopolymerization of fly ash, mixture proportioning of concretes containing fly ash alone as the binder, methods to improve the reactivity of fly ash through nanomodification or the use of fine limestone, and phosphate-based cements. Also, novel methods of the use of waste glass powder and rice husk ash as cementing materials are detailed. These paper are a useful addition to the library for any researcher, materials producer, or end user interested in alternative and sustainable binding materials for concrete. This CD consists of 8 papers that were presented at a technical session sponsored by ACI Committees 130. 232, and 236 at the ACI Convention in Dallas, TX, in March 2012. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-294

10.14359/51685950


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