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Showing 1-10 of 583 Abstracts search results

Document: 

SP-336_01

Date: 

December 11, 2019

Author(s):

James Lafikes, Rouzbeh Khajehdehi, Muzai Feng, Matthew O’Reilly, David Darwin

Publication:

Symposium Papers

Volume:

336

Abstract:

Supplementary cementitious materials (SCMs) in conjunction with pre-wetted fine lightweight aggregate to provide internal curing are being increasingly used to produce high performance, low-shrinking concrete to mitigate bridge deck cracking, providing more sustainable projects with a longer service life. Additionally, the SCMs aid in concrete sustainability by reducing the amount of cement needed in these projects. This study examines the density of cracks in bridge decks in Indiana and Utah that incorporated internal curing with various combinations of portland cement and SCMs, specifically, slag cement, Class C and Class F fly ash, and silica fume, in concrete mixtures with water-cementitious material ratios ranging from 0.39 to 0.44. When compared with crack densities in low-cracking high-performance concrete (LC-HPC) and control bridge decks in Kansas, concrete mixtures with a paste content higher than 27% exhibited more cracking, regardless of the use of internal curing or SCMs. Bridge decks with paste contents below 26% that incorporate internal curing and SCMs exhibited low cracking at early ages, although additional surveys will be needed before conclusions on long term behavior can be made.


Document: 

SP326-108

Date: 

August 10, 2018

Author(s):

Francesco Bencardino and Mattia Nisticò

Publication:

Symposium Papers

Volume:

326

Abstract:

Composite materials that employ modified cement-based mortars are usually named Fabric-Reinforced Cementitious Matrix (FRCM). The two main components are the cementitious matrix and the reinforcement fabric. The matrix can contain silica fume, blast furnace slag, fly ash and in some cases chemical property that can act as corrosion inhibitor. Some types of fabrics commonly used for the strengthening of existing Reinforced Concrete (RC) structures include nets with carbon or polyparaphenylene benzobisoxazole fibers disposed along one or two orthogonal directions, and unidirectional steel ropes (S-FRCM).

The S-FRCM system can be applied according to the traditional Externally Bonded (EB) or the innovative Inhibiting-Repairing-Strengthening (IRS) technique. The latter is a sustainable strengthening method and it is a useful solution for existing RC structures with deteriorated or damaged cover concrete.

Experimental tests show that for S-FRCM systems, applied with EB or IRS technique, the debonding occurs at fiber-matrix interface without significant damage at concrete substrate. Consequently, the debonding strain depends mainly by geometric and mechanical properties of external reinforcement and elastic/fracture properties of fiber-matrix interface. Considering experimental data available in literature, related to RC beams strengthened in flexure using S-FRCM systems, a predictive strain debonding relationship is defined and its reliability is evaluated through comparison between experimental and theoretical ultimate load.


Document: 

SP326-08

Date: 

August 10, 2018

Author(s):

Ojedokun Olalekan and P.S. Mangat

Publication:

Symposium Papers

Volume:

326

Abstract:

An Investigation on the mineralogical and chemical characterization, pore structure, chemical shrinkage and pozzolanic activity of commercially produced rice husk ashes (RHA 1 and 2) and a control silica fume (SF) are presented in this paper. RHA possesses high silica content like silica fume which is used as supplementary cementitious materials (SCM) in the production of concrete. There is a need for an alternative to silica fume in the production of concrete because of its high demand and relatively high cost.

The mineralogical composition of RHA 1 and 2 show high silica content of 77% and 84% respectively which is close to the silica content (˃80%) of class 2 silica fume. The oxides of Ca are 3.53% and 7.68% while Al is 1.19% and 1.29% for RHA 1 and 2 respectively which suggest that RHA is a low Ca+2 content binder. The results of chemical shrinkage of RHA 1, 2 and SF are 0.42 mL/g, 0.52 mL/g and 0.11 mL/g after 500 hrs of hydration. This indicates that RHA 2 has the highest reactivity (hydration) with water due to its highest Ca+2 content.


Document: 

SP-320_15

Date: 

August 1, 2017

Author(s):

Frank Winnefeld, Lukas H.J. Martin, Elsa Tschopp, Christian J. Müller and Barbara Lothenbach

Publication:

Symposium Papers

Volume:

320

Abstract:

Calcium sulfoaluminate (CSA) cements are receiving increasing interest because they promise to provide a low–CO2 alternative to portland cement. In order to save costs and to further reduce the amount of CO2 attributed to the production of CSA, they are often blended with supplementary cementitious materials (SCMs) such as limestone powder or industrial by-products such as slag or fly ash. In portland cement systems, pozzolanic SCMs react with portlandite to form C-S-H. In CSA cements this reaction path is not possible as portlandite is generally not present in the hydrate assemblage. In this contribution, thermodynamic modelling is used to assess how pozzolanic SCMs may contribute to the hydration reactions and change the hydrate assemblage of CSA cements. The calculated hydrate compositions are compared to experimental data proving that pozzolanic SCMs are able to contribute to the hydration reactions of CSA cements.


Document: 

SP-320_18

Date: 

August 1, 2017

Author(s):

Andrew Fahim, Edward G. Moffatt and Michael D.A. Thomas

Publication:

Symposium Papers

Volume:

320

Abstract:

This paper presents results obtained from steel-reinforced concrete specimens retrieved after 25 to 27 years of exposure in a marine environment. The specimens included mixtures with various SCM blends (25% fly ash, 10% silica fume and 50% slag), as well as a mixture without any SCM, all at a W/CM of 0.50. Testing included chloride-ion depth determination, rapid chloride permeability test, bulk electrical resistivity test and electrochemical corrosion-monitoring. The chloride profiles revealed that SCM incorporation leads to a significant decrease in chloride-ion penetration, which was supported by rapid chloride permeability and bulk electrical resistivity tests. Electrochemical corrosionmonitoring showed passivity for all reinforcements at a cover depth of 70 mm or more for specimens incorporating SCMs, while for specimens not containing SCMs, all reinforcements, up to a cover depth of 140 mm, showed active corrosion. Finally, it was found that the reinforcement corrosion rate in SCM concrete was significantly lower than that for portland cement concrete.


Document: 

SP-320_09

Date: 

August 1, 2017

Author(s):

Gabriel Medina, José María Medina, Isabel F. Sáez del Bosque, Moisés Frías, María Isabel Sánchez de Rojas, César Medina

Publication:

Symposium Papers

Volume:

320

Abstract:

This study assesses the pozzolanic activity of two types of waste, one from biomass power plants and the other from the ornamental granite industry. These materials were first characterised chemically, physically, morphologically and mineralogically. Pozzolan reaction kinetics in the waste/portlandite system were then researched by analysing the crystalline compounds with instrumental techniques such as TGA and XRD. The findings showed that bioenergy plant waste exhibited pozzolanic activity comparable to the values reported for other agri-forest additions and greater than recorded for fly ash. Activity in the granite industry waste, in turn, was greater than in fly ash and lower than in silica fume and New Additions for the Design of Eco-Efficient Cements. Analysis of Pozzolanic Reaction Kinetics 9.3 sanitaryware waste. In light of these results, both types of waste would potentially be apt for use as additions in eco-friendly cements.


Document: 

SP317-05

Date: 

June 1, 2017

Author(s):

M. F. Najjar, A. M. Soliman, T. M. Azabi and M. L. Nehdi

Publication:

Symposium Papers

Volume:

317

Abstract:

Sulfate attack is one of the aggressive damage mechanisms that can jeopardize the durability of concrete structures. Several research studies have investigated the positive influence imparted by supplementary cementitious materials (SCMs) regarding the resistance of conventional concrete to sulfate exposure. However, the effects of SCMs on the sulfate resistance of two-stage concrete (TSC) has not been duly explored. In this paper, the durability of TSC mixtures incorporating different SCMs, including fly ash (FA), silica fume (SF) and metakaolin (MK), as partial replacement for ordinary portland cement (OPC) was investigated. Two different sodium sulfate exposure regimes were simulated: full immersion (conducive to chemical sulfate attack) and partial immersion combined with cyclic temperature and relative humidity (conducive to physical salt attack). Results show that TSC specimens incorporating FA achieved acceptable resistance to chemical sulfate attack, while incurring severe surface scaling under physical salt attack. Moreover, TSC specimens made with MK exhibited adequate resistance to both chemical and physical attacks. Surprisingly, TSC specimens incorporating SF deteriorated significantly due to abundant thaumasite formation. An attempt is made herein to delineate the mechanisms that result in deterioration.


Document: 

SP314-06

Date: 

March 1, 2017

Author(s):

Anant Parghi and M. Shahria Alam

Publication:

Symposium Papers

Volume:

314

Abstract:

The aim of this study is to investigate the physical and mechanical properties of cement mortar by replacing a portion of cement with incinerated sludge ash (SA) and silica fume (SF) at different proportions. The experimental program consists of four series. In series-A, the substitution amounts include 0%, 5%, 7.5%, 10%, 12.5% and 15% of SA. In addition, in series A, B, C and D of the experimental program, 0%, 10% 15% and 20% of SF were added, respectively. The tests performed include consistency, setting time, flow table spread value, flexural strength (Rf), compressive strength (Sc), apparent bulk density, water absorption and sorptivity. The results show that the initial and the final setting times and workability increased, when the percentage of SA was higher. Due to little pozzolanic reaction, the strength activity index (SAI), and the initial compressive and flexural strengths of SA mortar decreased. However, addition of SF to SA mortar could improve its mechanical properties. Statistical analysis is also conducted to forecast the flexural and compressive strengths of mortar, and an equation is proposed by performing regression analysis.


Document: 

SP-308-09

Date: 

June 1, 2016

Author(s):

Francisco J. Presuel-Moreno, Eric I. Moreno

Publication:

Symposium Papers

Volume:

308

Abstract:

The aim of this study was to determine the chloride threshold concentration of carbon steel rebar embedded in high performance concrete under exposure conditions relevant to the substructure of coastal bridge in Florida. The experiments were based upon a series of reinforced and non-reinforced concrete specimens that contained 1) 20, 35 and 50 percent cement replacement by fly ash, 2) 6, 15 and 27 percent cement replacement by silica fume, and 3) control specimens (no pozzolanic admixture). All specimens had a target w/cm ratio of 0.37. The specimens have been exposed to one week wet - one week dry ponding cycle with natural seawater since January, 1995. Rebar potential values were monitored with time in order to determine when corrosion initiated. The rebar of several specimens activated after 15.6 to 17 years of exposure, and selected specimens were terminated for forensic examination and extent of corrosion. Cores were obtained to determine the extent of chloride ingress, the apparent diffusion coefficient (Dapp) and concrete resistivity. The chloride concentration above the rebar trace was also measured on most of the terminated specimens. The value for Dapp was correlated against the corresponding measured resistivity. Specimens with 50 percent FA had the lowest Dapp but also the lowest chloride threshold.


Document: 

SP305-33

Date: 

September 1, 2015

Author(s):

Valeria Corinaldesi and Giacomo Moriconi

Publication:

Symposium Papers

Volume:

305

Abstract:

In this work, fiber reinforced SCLWAC (self-compacting lightweight aggregate concrete) mixtures were studied, in which synthetic fibers were used. Eight different SCLWAC mixtures were prepared, by employing either fly ash or silica fume as mineral addition. In particular, as aggregates, different combinations of fine and coarse expanded clay were tried, also partially replaced by either quartz sand or recycled aggregate coming from a recycling plant, in which rubble from concrete demolition are suitably treated. The SCLWACs were characterized at the fresh state by means of slump flow, V-funnel and L-box tests, and after hardening by means of compression, splitting tension and bending tests, as well as drying shrinkage measurements. Strength class of LC 45/50 was obtained by using synthetic macrofibres when the oven dry density of SCLWAC was about 1600 kg/m3 [2700 lb/yd3], while if the oven dry density of SCLWAC was lower than 1250 kg/m3 [2100 lb/yd3] a strength class of LC 25/28 was reached as well. Splitting tensile and flexural strength measured values were consistent with concrete strength class, while the elastic modulus was quite low with respect to normal weight self-compacting concrete (SCC). The post-cracking behaviour of SCLWAC resulted strongly improved by the addition of synthetic macrofibers, which proved to guarantee a softening behaviour in flexure. In conclusion, the addition of synthetic fibers allowed to design special concretes with excellent combination of mechanical and functional properties.


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