bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Mix Design on the Properties of Sulfur Concrete
Authors: Czarnecki B , Gillott JE
Published: January 2010

Some sulfur concretes have been shown to expand excessively under moist conditions. The deterioration is accompanied by a decrease in dynamic modulus of elasticity with time. The durability of sulfur concretes containing glycerin and crude oil admixtures was slightly improved, but expansions were still unacceptably high. Two silane admixtures significantly decreased the moisture expansions. Silane type A was more effective when larger amounts were used, but differences in amount of silane type Z had little effect on amount of expansion. Silanes also improved the durability of sulfur concrete when assessed by the dynamic modulus of elasticity, which generally remained at the same level during water immersion. It is concluded that by changing the surface characteristics at the aggregate-sulfur interface silanes minimize the detrimental effects of moisture.
The Creep of Concrete Pipes in Kuwait
Authors: Al-Obaid YF
Published: January 2010

Most concrete pipes of 915-mm diameter buried 1.5 m below the surface of Kuwait highways have been examined. About 55% of these developed circumferential strains (in tension) about 30 microstrain at top and bottom as soon as they were buried. In a matter of eight weeks, due to vehicle loads, the top strains increased on 100 pipes by 10% and bottom strains remained unchanged. An experiment has been carried out on site to determine the magnitude of the creep occurring in such pipes. In a period of six months the creep strains have increased by three times the previous strains resulting from the initial application of loads. Over 60% of the concrete pipes tested show 4.75 times creep strains measured at the initial stages. On King Faisal Road some pipes on removal indicated a substantial degradation of material due to sulfur attack.
Anisotropy of Concrete Strength
Authors: Leshchinsky AM
Published: January 2010

Results obtained by numerous researchers concerning concrete strength anisotropy are analyzed. In some cases, the researchers have found that the compressive strength of specimens loaded at a right angle to a direction of concrete placing, f′c, is greater than for those loaded parallel to the above direction, f″c; in other cases, it is lower. This fact has been elucidated. In the cases where anisotropy is caused by the “internal” mix segregation, we come across f′c/f″c > 1; when the cause is in the “external” mix segregation, the result is f′c/f″c < 1. Given are recommendations for taking into account such anisotropy in core testing.
Crack Counts in Air-Entrained and Non-Air-Entrained Concrete Subjected to Accelerated and Fog-Room Curing
Authors: Gillott JE , Czarnecki B
Published: January 2010

Concrete cured by the accelerated steam method, at atmospheric pressure, sometimes shows a reduced rate of strength gain at later ages. This loss of potential strength has been attributed to a number of factors, including microcracking caused by differential stress within the material. This may result from differences in the thermal expansion coefficients of the solid phases themselves and from the greater differences between the coefficients of solids and water. Because entrained air voids help to protect concrete from damage by frostaction by providing void spaces that reduce the build-up of hydraulic pressure caused by migrating water, we postulated that entrained air may similarly benefit concrete subjected to accelerated steam curing. The loss of potential strength in the steam-cured specimens was assumed to result from an increase in internal microcracking.

Specimens of air-entrained and non-air-entrained concrete were made and subjected to fog-room curing and to accelerated steam curing. However, crack-counts made at ages of 1 day and 28 days under an optical microscope were similar in both air-entrained and non-air-entrained concrete. At 28 days, crack-counts were higher in the fogcured concrete than in the steam-cured concrete whether air-entrained or not. Consequently, the data did not support the suggestions that entrained air would reduce internal stresses and resulting microcracking. Also, regardless of air-entrainment, it was found that crack counts were highest in samples that had gained strength most rapidly.
Optimization of the Composition of a High-Performance Concrete
Authors: Rougeron P , Aïtcin P-C
Published: January 2010

The production of a high-performance concrete (HPC) is more of an art than a science, although the basic principle needed to be implemented is simple: HPC is a concrete having a low waterbinder ratio (W-B). Achieving a low water-binder ratio can be realized in many different ways. The work reported hereafter tries to answer three basic questions:

• Is it better to use the least amount possible of mixing water with a high dosage of superplasticizer to obtain the desired workability, or is it better to use more water (and more cement), but less superplasticizer?

• Is the use of silica fume advantageous in making HPC?

• If yes, what is the maximum price that can be paid for it?

A factorial design plan involving 18 laboratory concrete batches has shown that the use of silica fume is advantageous up to a price of $600/ton (CAN) (for the conditions of the experiment). Moreover, it was found that for a precast operation, it is better to increase the amount of water used in making HPC and to decrease the amount of superplasticizer; for the ready mix operation, the reverse is true.

Silica fume and the superplasticizer employed were shown to be effective fluidifying agents, although they did slightly increase the time at which maximum compressive strengths were reached. Erratum to this paper appears in 17(1).
Determination of Water Content of Fresh Concrete Using a Microwave Oven
Authors: Nagi M , Whiting D
Published: January 2010

As part of the Strategic Highway Research Program (SHRP) contract, Optimization of Highway Concrete Technology, a microwave-oven method for measuring water content of as-delivered fresh concrete was evaluated. Water contents of a series of concrete mixes prepared in the laboratory were gravimetrically determined by drying the concrete in a microwave oven and comparing these measurements with water contents used for making these mixes. A relatively high-power microwave (900 W) equipped with a turntable to provide uniform drying was used. Mixes used in the study included conventional concrete mixes with three types of aggregates with low, moderate, and high water absorptions and mixes with silica fume, fly ash and latex. Field ruggedness of the procedure was verified by testing under actual field conditions at placements of bridge deck overlays and full-depth pavement repair sections.

Test results showed that this technique is sufficiently reproducible for purposes of field control and is independent of absorption of aggregates or consistency of concrete. The test is quite simple and does not require a skilled operator. The total test time is 16 min, including time for sample manipulation and check-weighing twice during the drying process. The method can be applied to latex-modified and silica-fume concretes, as well as more conventional mixes.
The Effects of Different Cementing Materials and Curing on Concrete Scaling
Authors: Afrani I , Rogers C
Published: January 2010

As part of a project to determine the long-term durability of concrete made with an alkali-silica reactive coarse aggregate, six concrete mixtures were made with a variety of cementing materials: high-alkali portland cement (HAPC), low-alkali portland cement (LAPC), 25% ground granulated blast-furnace slag (GGBFS), and 50% GGBFS with high-alkali portland cement, 18% Type F fly ash with high-alkali portland cement, and 3.8% silica fume with high-alkali portland cement and 25% GGBFS. Concrete slabs were cast and cured under three conditions: 14 days in the moist room at 23°C, 14 days outdoors covered under wet burlap and plastic sheet, and 28 days in the laboratory air after application of a curing compound. The slabs were tested at an age of 28 days for 50 freeze-thaw cycles in the scaling test using a 3% sodium-chloride (NaCl) solution. The slabs cured outside under wet burlap generally had a high resistance to scaling, with the exception of the mixture with 50% GGBFS. This concrete also exhibited scaling of a full-scale outdoor slab on grade during the first winter. The slabs cured, according to the test method, in the moist curing room generally showed a low resistance to salt scaling. Erratum to this paper appears in 17(1).
Mineral Admixtures Contribution to the Development of Heat of Hydration and Strength
Authors: Rahhal VF , Batic OR
Published: January 2010

The heat of hydration of normal portland cement causes an increase in concrete temperature that may result in undesired cracks on cooling after hardening. For this reason, alternatives to lowering it are sought.

This paper discusses the benefits of adding mineral admixtures, such as natural pozzolan, fly ash, and granulated blast furnace slag to control heat of hydration development. For this study, blended cements were prepared using an ordinary portland cement clinker, gypsum, and mineral admixtures, previously ground in a laboratory mill. The average fineness employed was 450 m2/kg. The percentages of mineral admixtures were: 0, 10, 20, 30, 50, 70, and 90, by mass. Tests were performed at 3, 7, 28, 90, and 180 days. Results are expressed in percentages of control cement (0% replacement) and are plotted for each replacement, percentage, and age.

Empirical coefficients of the contribution of mineral admixtures to the heat of hydration have been obtained, as well as a mathematical expression to estimate the heat of hydration of a blended cement, on the basis of the mineral admixture selected, the percentage used, and the heat of hydration of the control cement, up to 180 days.
The Effect of Mold Size and Mold Material on Compressive Strength Measurement Using Concrete Cylinders
Authors: Day RL
Published: January 2010

Fourteen concretes were cast, with and without air entrainment and fly ash, using various sizes of cylindrical mold made from different materials. Cylinders were cured in the standard manner and tested for compressive strength, primarily at an age of 28 days. The range of strengths measured was 30 to 50 MPa. Each cast consisted of 60 cylinders, with 12 replicates performed for each of the five types of mold: 150-mm diameter cardboard and plastic molds (notation, C150 and P150); 100-mm diameter plastic molds (P100); and 75-mm cardboard and plastic molds (C75 and P75). The length/diameter ratio of all cylinders was 2.0.

For 150-mm cylinders, the variability of strength measurement, as indicated by the average coefficient of variation (cv), did not depend upon the type of mold material used (cardboard or plastic). For 75-mm cylinders, the same observation was made; cv did not depend upon mold-material.

However, when plastic molds were used, there were significant differences in cv as cylinder size varied. The average cv for P75 cylinders was 4.9 MPa, while it was 3.2 MPa for P150 cylinders; the increase is highly significant. On the other hand, P100 cylinders gave a cv of 3.6 MPa, which is not significantly different than that for P150 cylinders.

For cardboard molds, where 150- and 75-mm cylinders were tested, the cv was not a function of cylinder size.

The effect of mold material and diameter on the magnitude of measured strength was also examined. No distinct trends were observed. Differences in observed strengths due to type and size of mold were influenced by the type of concrete tested and the procedure for initial storage during the first 24 h of curing. However, when all 28-day strengths were considered in paired-t analyses, the following differences were found to be significant: (1) the use of 75-mm molds (C75 and P75) resulted in a higher strength of about 1 MPa, compared to the larger molds (P100, P150, C150); (2) for 150-mm molds, the use of plastic instead of cardboard resulted in a lower strength, about 1 MPa; and (3) the strength obtained from concrete cast into plastic molds increased as the mold size decreased; the difference between P100 and P150 molds was 1 MPa, while the difference between P75 and P150 molds was, on average, 1.6 MPa.

Some of the differences in strength among the mold types was traced to differences in moisture loss during the first 24 h of storage. Cylinders stored under plastic sheet (in accordance with the American Society for Testing and Materials (ASTM) specifications), were about 3 MPa stronger than those stored in sealed plastic bags (in accordance with the Canadian Standards Association (CSA) requirements). Erratum to this paper appears in 17(1).
Cement Strength Variations: Defining the Solution
Authors: Gebhardt RF
Published: January 2010

Strength is one of the most important properties of cement. When major strength variations occur, control actions are usually taken to mitigate the problem. The control actions taken can mask exactly when the deviations occurred and can hide their magnitude in addition to obscuring their source. It is often possible, however, to remove the effect of a known variable so that the source(s) of the problem can be located.

If strength values for individual production samples are divided by their fineness, the resulting values of strength per unit fineness (suitably indexed for readability) can be graphed versus time to determine exactly when strength deviations occurred (unrelated to fineness) and their magnitude. An example from an actual production problem illustrates the method and shows how the transformed data can be used to demonstrate the probable sources of the strength variations. Erratum to this paper appears in 17(1).
Effect of Capping Materials and Procedures on the Measured Compressive Strength of High-Strength Concrete
Authors: Lobo CL , Mullings GM , Gaynor RD
Published: January 2010

The effect of end conditions and testing procedures on the measured strength of 100- by 200-mm (4- by 8-in.) concrete cylinders were evaluated. Concretes representing three strength levels: 50, 75, and 120 MPa (7000, 11 000, and 17 000 psi) were prepared. Cylinder end conditions included grinding and capping with two types of sulfur mortar and cement paste. Effect of thickness of capping material was also evaluated.

Cement paste caps produced, on average, 1% higher strengths than ground ends, regardless of concrete strength level and cap thickness. Cylinders capped with sulfur mortar 2 h prior to testing produced 2 to 7% lower strengths than the ground condition. Capping cylinders with sulfur mortar seven days prior to testing produced strengths equivalent to the ground condition, except with thick caps of sulfur mortar on the 120 MPa (17 000 psi) concrete, in which case lower strengths were observed. No significant difference between sulfur mortars was evident, even though one was advertised for use with high-strength concrete.
Strength Evaluation of In-Situ Concrete by Rebound Hammer and Core Testing
Authors: Ward MA , Langan BW
Published: January 2010

This paper describes the results of an extensive field investigation where the quality of in-place concrete flatwork was evaluated. Nondestructive testing (NDT) was carried out using ultrasonic pulse velocity and rebound hammer techniques to establish a correlation with compressive strengths of core tests. The rebound hammer/core correlation formed the basis of a recommendation on the acceptance or rejection of the in-situ concrete. The ultrasonic pulse velocity UPV testing was primarily used to establish concrete uniformity. Limited freeze-thaw testing was carried out to determine the potential long-term durability performance. In order to minimize the effects of surface preparation on the test results, considerable time was spent to determine the optimum grinding procedure.
Break-Off Test for High-Strength Concrete
Authors: Di Maio A , Giaccio G , Zerbino R
Published: January 2010

High-strength concrete is one of the new developments in concrete technology. In addition to compressive strength levels above 60 MPa, high workability, improvements in early age performance and durability appear to be its main advantages. This paper studies the suitability of the break-off test to evaluate strength development of high-strength concrete. Regression equations between break-off pressure and compressive strength were calculated. The effects of different variables such as age, type of coarse aggregate, and strength level are discussed. The obtained results indicate that the break-off test can be used satisfactorily to evaluate the quality of concretes with compressive strength levels up to 100 MPa.
Comparison of Five Standards on Ultrasonic Pulse Velocity Testing of Concrete
Authors: Komlos K , Popovics S , Nurnbergerova T , Babal B , Popovics JS
Published: January 2010

The essence of the pulse velocity method is that the transition time of an ultrasonic longitudinal pulse (wave) is measured in concrete. From this, the pulse velocity can be calculated, and inferences are drawn concerning the strength or overall quality, or both, of the concrete. Many countries have standardized this procedure, five of which are compared in this paper. These are American (ASTM), British (BS), German (DIN), Russian (GOST), and Slovak (STN) standards.

The best, and perhaps the only reliable applications of the ultrasonic pulse velocity are for checking the uniformity of concrete and monitoring the changes in a concrete with time. Strength estimation is possible with only ±20% accuracy and even this can be achieved only under strict laboratory conditions. The other applications (defect detection, crack depth measurements, and so forth) are even less reliable. Thus, they are inadequate for practical purposes, especially under field conditions. No warning is given in any of the examined standards about the unreliability of most of these applications.

It is hoped that an evaluation of these standards will help in the better use of the ultrasonic pulse velocity method and contribute to the improvement of future standards.
Improving Initial Strength of a Concrete made with Type 20M Cement
Authors: Kessal M , Nkinamubanzi P-C , Tagnit-Hamou A , Aïtcin P-C
Published: January 2010

The improvement of initial strength of concrete constitutes a special interest for contractors that often seek to enhance their productivity by reducing the delay before deforming. The study presented in this paper shows that it is possible to use a low heat of hydration Type 20M cement that is typically employed in Quebec in mass concrete construction to develop high initial strength that can be of special interest in enhancing the production of massive structural elements. Type 20M cement is similar to Type II ASTM cement but has a slightly lower heat of hydration.

The improvement of initial strength of concrete made with Type 20M cement was made possible by reducing the W-C ratio by using a melamine-based superplasticizer that has less influence on retarding the setting time than that of a naphthalene-based superplasticizer and by substituting part of the cement by an adequate amount of silica fume and limestone filler.
Evaluation of Laboratory Drying Procedures Relevant to Field Conditions for Concrete Sorptivity Measurements
Authors: DeSouza SJ , Hooton RD , Bickley JA
Published: January 2010

The surface humidities of a limited set of field concretes during summer conditions in Ontario were measured prior to water absorption (sorptivity) testing. A series of alternative laboratory curing conditions was carried out on cores prior to laboratory sorptivity tests, to determine which would best mimic average field conditions (surface humidities greater than 40% and moisture contents greater than 1%). It was found that three days' oven drying at 50°C followed by sealed drying for four days at 50°C as suggested by Parrott worked well. In addition, the moisture content at test was calibrated to measured sorptivity results.
Hydrogen Evolution in Concrete Due to Free Silicon Metal in Microsilica
Authors: Fidjestøl P , Jørgensen O
Published: January 2010

Many millions of cubic meters of microsilica concrete have been placed over the years. Still, concern has been raised over possible risks related to the formation of hydrogen due to free silicon metal (silicon) contained in microsilica (silica fume, condensed silica fume).

The paper addresses this question from four different viewpoints: • Chemical reaction mechanism and theoretical amounts of hydrogen that can be generated. • Definition of explosion limits on hydrogen content in the air. • Test method for silicon-metal content in microsilica in one laboratory and comparison between laboratories. • Hydrogen development in practical situations, that is, in tests with mortar in an isolated chamber and in simulation tests of hollow-core elements.

From the present study it is concluded that only in extreme cases, with very high silicon-metal contents and with heat curing, can sufficient hydrogen be developed to cause an explosive mixture of gases. Further, the limit of 0.4% metallic silicon, as determined by the recommended method, will remove even these concerns.
An Overview of the Fracture Mechanics of Concrete
Authors: Shah SP
Published: January 2010

For the design of concrete structures where adequate ductility is a concern, it is becoming increasingly necessary to use concepts based on crack growth and propagation to account for ductility and avoid catastrophic failure. While fracture based methods exist for steel design, no standard method currently exists to quantify the fracture properties of concrete. In light of a multitude of recent investigations to describe the complex nature of concrete fracture, it is currently accepted that two parameters are required to characterize crack propagation in concrete. This paper provides a brief background for the use of fracture mechanics in concrete and appeals for the establishment of standardized testing procedures for use in concrete. If appropriately determined, fracture parameters can provide a valuable tool for the design of new higher performance concretes and concrete structures.
Fracture Mechanics Testing for Structural Steels
Authors: Rolfe S
Published: January 2010

Fracture mechanics is widely used to evaluate the fracture behavior of structural steels. However, the fracture toughness of structural steels is affected significantly by temperature, loading rate, and constraint. Because of the effect of these factors, the fracture behavior of structural steels varies considerably from linear elastic to general yielding. Accordingly, there are numerous fracture mechanics tests of structural steels—each of which is applicable to the general regime of linear-elastic, elastic-plastic, or general yielding behavior.

This paper describes the fracture testing and behavior of structural steels in each of these three general domains and briefly describes the ASTM test methods used in each domain.
Standards for Fracture Toughness Testing of Rock and Manufactured Ceramics: What Can We Learn for Concrete?
Authors: Hanson JH , Ingraffea AR
Published: January 2010

This paper presents a review of the American Society for Testing and Materials (ASTM) and the International Society for Rock Mechanics (ISRM) standards for determining the plane-strain fracture toughness of cemented carbides and rocks, respectively, with an eye toward applicability to concrete. The evolution of the chevron-notched test specimen used in these standards is briefly reviewed. A discussion of a particular chevron-notched configuration, the short rod test specimen, and associated test methods follows. The ASTM and ISRM standards are then described. The paper evaluates the potential for learning from, modifying, or adapting these standards for use on a standard fracture toughness test for concrete. The potential advantages and disadvantages of using the short rod geometry and testing methods on concrete are discussed, taking into account fracture response, shape, volume, preparation, precracking, symmetry, and subsize specimen effects. Preliminary research into the applicability of the short rod geometry and testing procedures on concrete is discussed.
Determination of Slag and Fly Ash Content in Hardened Concrete
Authors: Hooton RD , Rogers CA
Published: January 2010

Some agencies limit the slag (ground-granulated blast-furnace slag) replacement of portland cement in some instances. In other cases, minimum slag replacements are specified. Therefore, there is a need to be able to quantify the slag content to show conformance with specifications. The two methods proposed here are (1) X-ray diffraction (XRD) of ignited mixtures and (2) optical microscopy on thin sections. The XRD method involves ignition of the mortar fraction of concrete at 950 to 1050°C to devitrify the unreacted slag. The resulting crystalline melilite component is then compared to that in an ignited sample of slag from the same source.

The optical method involves preparation of thin sections of the concrete and point counting to obtain the number of unhydrated slag grains. These are compared to a set of calibration standard sections. The optical technique can also be used for estimating fly ash content and similarly, grain mounts have been used to detect the presence of both fly ash and slag substitution in portland cements.

The paper describes both these techniques in detail and discusses limitations. When properly calibrated, either technique can be used to estimate the slag replacement level to approximately ±10%. As well, several case histories are described where these procedures have proved to be extremely useful.
Determination of Slag and Pulverized Fuel Ash in Hardened Concrete—The Method of Last Resort Revisited
Authors: Grantham MG
Published: January 2010

The paper briefly reviews the standard United Kingdom (UK) procedure for the determination of cement content of hardened concrete. It then points out the special problems that occur when attempting to determine the cement content and the amount of mineral admixture in concrete. The method described in this paper, originally devised by the Building Research Establishment, employs a total analysis of the concrete and control samples of the cement, aggregates, and mineral admixture. The method usually used is quantitative X-ray fluorescence (XRF) analysis. The analytical results are examined by the application of a simultaneous equation mathematical approach to resolve the content of the individual components. Application of the method in a case history is used for illustration.
Chloride Permeability Versus Air Content of Latex Modified Concrete
Authors: Kuhlmann LA , Foor NC
Published: January 2010

Results of chloride permeability tests on latex modified concrete (LMC) with a wide range of air contents are presented. Air void data from these experiments are compared to air void results from other sources. Conclusions regarding chloride permeability and the air void system of LMC are given. The 6-h permeability test is described; comments are made regarding an additional measurement to be considered for inclusion in the method. Recommendations are given for future study of the chloride permeability of LMC.
Recycled Concrete—A Source for New Aggregate
Authors: Rasheeduzzafar  , Khan A
Published: January 2010

Recycling concrete rubble as aggregate material for the construction programs in the Middle East, where high-quality mineral aggregate is scarce, offers an excellent ecological and economic opportunity. Based on tests carried out on 21 mixes, this investigation attempts to develop data especially on the strength, failure mechanism, and durability characteristics of the recycled aggregate in comparison with the conventional concrete. Results show that for a W/C ratio of 0.35 the recycled aggregate concrete has 30% lower strength than conventional concrete. The strength differential narrowed for increasing values of W/C ratio until the strengths were about equal for a W/C ratio of 0.55. No significant increase in the strength of recycled aggregate concrete was obtained by reducing the W/C ratio below 0.40. It is indicated that the quality of recycled aggregate concrete will improve with the quality of recycled mortar or if the recycled material has a high aggregate-cement ratio. The recycled aggregate concrete showed somewhat better workability characteristics than conventional mixes although its modulus of elasticity and durability characteristics were lower. It is proposed that satisfactory concrete can be made by recycling concrete as aggregate where disposal problems exist or where natural aggregate is either inaccessible or of inferior quality.
The Variability of Condensed Silica Fume from a Canadian Source and Its Influence on the Properties of Portland Cement Concrete
Authors: Pistilli MF , Rau G , Cechner R
Published: January 2010

Condensed silica fume is formed during the manufacture of ferrosilicon in electric submerged-arc furnaces. The use of condensed silica fume has been evaluated in portland cement concrete. Thirty-two samples of condensed silica fume, each collected on consecutive days, were analyzed for chemical and physical routine quality control tests of pozzolan. Eight of these samples, representing the variations of the routine tests, were tested for complete ASTM Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete (C 618) conformance. All of the samples tested were found to conform to ASTM C 618 with the exception that the water requirement was excessive.

Concrete mixtures were evaluated with a fixed quantity of 24 kg/m3 (40 lb/yd3) of condensed silica fume. The low portland cement content mixtures show slightly higher shrinkage after 64 weeks of drying; the rich mixtures have the same shrinkage. Compressive strengths were more than 30% higher than control mixtures having low cement contents and were more than 10% higher than control mixtures having higher cement contents. This amount of condensed silica fume was found to have no effect on the time of set relative to control mixtures containing the same portland cement content.
On In-Place Strength of Concrete and Pullout Tests
Authors: Yener M , Chen W-F
Published: January 2010

The current status of in-place strength evaluation of concrete is discussed. A literature survey regarding the controversy surrounding the assessment of concrete strength through field-cast laboratory-cured cylinder tests is presented. Inconsistencies associated with the drilling and testing of cores for determining in-place concrete strength are pointed out. On the basis of these arguments, the necessity of developing alternative nondestructive test procedures is emphasized. This is followed by a detailed discussion on the status of the pullout test method as a measure of compressive strength of in-place concrete, which appears to be a potentially feasible nondestructive test procedure. The present paper constitutes a state of the art report on the aforementioned topics and contains appropriate recommendations from the authors.
The Uniformity and Influence of Silica Fume from a U.S. Source on the Properties of Portland Cement Concrete
Authors: Pistilli MF , Wintersteen R , Cechner R
Published: January 2010

Silica fume is formed during the manufacture of ferrosilicon in electric submerged-arc furnaces. The use of silica fume has been evaluated in portland cement concrete. Thirty samples of silica fume, each collected on consecutive days from SKW Alloys, Inc. in Calvert City, KY, were analyzed for routine quality control tests of a pozzolan. Six of these samples, representing the variations of the routine tests, were tested for complete ASTM Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete (C 618) conformance. Laboratory mixtures of air-entrained and nonair-entrained concrete, containing a representative sample of silica fume, were cast for compressive strength (1 to 120 days), drying shrinkage, and time of set. Although a classification for silica fume is not currently contained in ASTM C 618, all of the samples tested were found to conform when compared to the requirements of this standard, with the exception that the water requirement was excessive.

Concrete mixtures containing only 24 kg/m3 (40 lb/yd3) of silica fume showed slightly high shrinkage at 64 weeks of drying with the lower cement content mixtures relative to control mixtures. The silica fume mixtures showed 120 to 180% higher compressive strength at 120 days in lean mixtures, 110 to 120% higher compressive strength in richer mixtures. This amount of silica fume was found to have no effect on initial set of concrete and had only a slightly longer final set.
A Rockwell Hardness Test for Concrete
Authors: Winslow DN
Published: January 2010

The standard superficial Rockwell 15Y hardness test has been adapted for use on concrete. Hardness measurements were made on the mortar regions between the coarse aggregate pieces. A correlation between this hardness and the concrete's compressive strength was developed. For 7.5- by 15-cm (3- by 6-in.) cylinders, it is Rockwell 15Y hardness = 73.5 (log compressive strength in psi) — 187 or 73.5 (log compressive strength in MPa) — 28.0. Various effects of specimen preparation and size are discussed, as are the statistics of the test.
Mechanism of Pozzolanic Reactions and Control of Alkali-Aggregate Expansion
Authors: Bhatty MSY
Published: January 2010

The mechanism of pozzolanic reactions and their control of expansion caused by alkali-aggregate reaction was investigated. Mixtures of tricalcium silicate, opal, sodium hydroxide, and water having calcium oxide to silica mole ratios from 1.07 to 3.0 were prepared and reacted from seven days to four years before filtering. The solids (precipitates) were studied by X-ray diffraction to determine the phases present, and the alkali content of filtrates was obtained by chemical analysis.

Results suggest that pozzolans reduce or eliminate alkali-aggregate expansion by producing additional calcium silicate hydrate and low lime calcium silicate hydrate. These hydrates can retain additional alkali, thus reducing the amount of alkali available for reaction with reactive aggregate. In order to control alkali-aggregate expansion by the addition of pozzolan, such as fly ash, results indicate that about 30% low lime fly ash is required. However, this amount could be reduced considerably, to a level as low as 20% (cement basis), if the concrete contains reactive siliceous aggregate.
Nondestructive Combined Methods Applied to Structural Concrete Members
Authors: Di Maio AA , Traversa LP , Giovambattista A
Published: January 2010

Strength evaluation of structural elements has been done by nondestructive methods, using ultrasonic pulse velocity, hammer rebound, and localized pressure, either individually or in a combined way. The effects of the mineralogical composition of the coarse aggregate, moisture content, and age of concrete on pulse velocity and rebound number is reported. Standard cylindrical specimens cured at 100% relative humidity were tested for compressive strength. Regression equations thus obtained were used to estimate the in-situ compressive strength of reinforced prisms (0.15 by 0.15 by 1.00 m). The prediction error is calculated from the comparison of the estimated strength and the strength determined on drilled cores.
The Effect of Blast Furnace Slag Cement on Alkali Aggregate Reactivity: A Literature Review
Authors: Hogan FJ
Published: January 2010

The growing shortage of quality aggregates and the trend toward higher alkali levels in portland cement has increased the risk of problems associated with alkali-aggregate reactivity (AAR). The use of ground granulated blast furnace slag as a partial replacement for portland cement is a recognized remedial alternative in cases where a potential for AAR exists.

This report reviews available literature dealing with the influence of ground granulated blast furnace slag on AAR. In general, it was concluded that when the binder consists of 50% or more of ground vitreous slag, an alkali content of up to 1.00% as sodium oxide (Na2O) equivalents can be tolerated without a risk of problems. Improved resistance to AAR was provided from slags ground to higher fineness.

Several theories, promulgated to explain the mechanism for enhanced resistance to alkali reaction, are also reviewed.
Laboratory Examination of a High-Alumina Cement Concrete Column After 46-Years Exposure at Treat Island, Maine
Authors: Buck AD , Burkes JP
Published: January 2010

Examination of a high-alumina cement (HAC) concrete specimen made in the laboratory and exposed to several hundred cycles of freezing and thawing at Treat Island, ME, showed that its excellent durability was due to the fact that it was in fact air entrained. This was a surprise since it was supposed to be nonair-entrained concrete. The reason for this discrepancy is not known. In addition, X-ray diffraction examination showed that the phase conversion often associated with HAC had not occurred.
Practical Considerations Pertaining to the Microscopical Determination of Air Void Characteristics of Hardened Concrete (ASTM C 457 Standard)
Authors: Pleau R , Plante P , Gagné R , Pigeon M
Published: January 2010

Many parameters affecting the quality of the air void characteristics measurement are reviewed and discussed. The difficulties more frequently encountered during the measurement process are described, and some simple rules are proposed in order to increase, as much as possible, the accuracy and reproducibility of the test. The influence of the sampling size is studied, and the variability of air content, specific surface, and spacing factor is estimated from a statistical analysis of about 600 different concrete mixtures. The influence of the operator's subjectivity is also investigated, and the effect produced by large air voids on the computation of the spacing factor is discussed.
Results of an Interlaboratory Concrete Testing Program: Part I
Authors: Gray RJ
Published: January 2010

Measures of the within- and between-laboratory variability associated with the standard test method for determining the compressive strength of cylindrical portland cement concrete specimens have been derived from data obtained in three interlaboratory testing programs operating in western Canada. These data have been analyzed using appropriate ASTM standard practices to provide estimates of repeatability (within-laboratory) and reproducibility (between-laboratory) standard deviation values and corresponding precision indices (difference “two”-standard-deviation limits). Both measures of variability have been found to vary linearly with the compressive strength of the test concrete, and hence the standard deviation and precision values are best expressed as linear functions of this strength. The resulting reproducibility (between-laboratory) precision index values are particularly important in that they provide guidance as to the level of the component of variability to be expected when two or more laboratories are testing the same batch of portland cement concrete for its compressive strength.
Characterization of Ground Granulated Blast-Furnace Slags and Fly Ashes and Their Hydration in Portland Cement Blends
Authors: Douglas E , Elola A , Malhotra VM
Published: January 2010

Chemical analysis, glass content, particle size distribution, heat evolution rate and total heat evolved, scanning electron micrographs and strength development have been studied for three granulated blast furnace slags of different origin and two fly ashes of low and high CaO content.

At all ages heat evolution rates and total heat evolved by the fly ashes are lower than the corresponding values for the granulated blast furnace slags, regardless of their origin.

In the blends studied, high-lime-content fly ash develops higher compressive strengths than low-lime fly ash above the 25% portland cement replacement level.

The results of the study indicate that 50% portland cement replacement by the high-lime-content fly ash used may provide an acceptable compromise to obtain concrete with high compressive strength and low heat of hydration.
A Method for Proportioning High-Strength Concrete Mixtures
Authors: de Larrard F
Published: January 2010

This paper deals with the problem of proportioning high-strength concrete mixtures. An empirical formula is presented that allows the prediction of strength. Also presented is a theoretical model for predicting workability. A practical method is derived to determine the proportion of materials for high-strength concrete mixtures having certain specifications. In this method, it is assumed that the optimal concrete will have a low binder paste and a high admixture content. It is also supposed that the coarse aggregate is stronger than the paste. As most tests are performed on pastes, the number of trial batches and the quantity of materials used during the study are minimal. The concretes obtained by this method exhibit good secondary qualities.
Mechanical Properties and Workability of Superplasticized Concrete
Authors: Jerath S , Yamane LC
Published: January 2010

In the design of concrete structures, the modulus of elasticity, the modulus of rupture, and the split cylinder tensile strength of concrete are predicted from its compressive strength. In this paper, the relationship between compressive strength and other mechanical properties is studied for superplasticized concrete with W-C ratios of 0.28, 0.35, 0.45, and 0.55. Also in this study, the effect of different dosages of a high-molecular-weight sulfonated naphthalene condensate superplasticizer known as Lomar-D on the compressive strength, stress-strain relationship, modulus of elasticity, Poisson's ratio, modulus of rupture, and split cylinder tensile strength of normal, medium, and high-strength concrete mixes is investigated. Overall, 72 cylinders and 36 beams were tested in accordance with ASTM specifications. In addition, the effect of different dosages of the superplasticizer on the workability of different mixes and the slump loss with time was also measured.
Finite-Element Analysis of the Pullout Test Using a Nonlinear Discrete Cracking Approach
Authors: Hellier AK , Sansalone M , Carino NJ , Stone WC , Ingraffea AR
Published: January 2010

An axisymmetric finite-element model, in which fracture was simulated by means of a nonlinear discrete cracking approach, was used to study the pullout test. The pullout test involves measuring the force required to extract a conical frustum of concrete by pulling on an embedded steel disk in opposition to a concentric steel reaction ring at the concrete surface. The precise mechanism of failure and therefore the strength property of concrete, which is actually being measured by the pullout test, has been the subject of several recent studies. The present analysis indicates that failure initiates with the formation of a stable, primary crack system extending from the outer edge of the insert to a point beneath the reaction ring where it is arrested. A stress redistribution resulting from this cracking leads to the development of a secondary crack system which initiates below the concrete surface at the inner edge of the reaction ring and propagates towards the outer edge of the insert. This secondary crack system becomes the eventual failure surface defining the conical frustum. The failure surface appears to be completed by shear fracture of the remaining uncracked ligament. The ultimate load-carrying mechanism is aggregate interlock across the completed failure surface.
Application of the Rapid Chloride Permeability Test to Evaluation of Penetrating Sealers for Concrete
Authors: Whiting D
Published: January 2010

Specimens for rapid and long-term (90-day) chloride permeability measurements were prepared from a conventional concrete mixture. Three penetrating sealers were evaluated, using different methods of specimen conditioning. Results indicate that the rapid chloride permeability test may indicate differences between sealers which are not apparent when subjected to long-term chloride ponding. The method chosen to condition the specimens prior to testing has a significant influence upon the results.
Correlation Between Materials Finer Than No. 200 Sieve and Sand Equivalent Tests for Natural and Crushed Stone Sands
Authors: Alhozaimy AM
Published: January 2010

Fine aggregates used in ready-mixed concrete industry in Riyadh (the capital city of Saudi Arabia) are mainly blended of natural silica sand and manufactured sand obtained from crushed limestone. Fine materials (clay, silt, or dust content) are one of the most important defects of aggregate in Riyadh, particularly in crushed sand. In ready-mixed concrete plants (RMC) and independent laboratories in Riyadh, the practice of determining the amounts of fine materials in fine aggregates is either by ASTM C 117 (materials finer than No. 200 sieve by washing) or ASTM D 2419 (sand equivalent test) and sometimes both.

In this paper, the relationship between the sand equivalent and materials finer than No. 200 sieve tests was investigated. A total of 100 samples of natural silica sand and 100 samples of crushed sand were collected from the stock-piles of different ready mixed-concrete plants in Riyadh. Also, the effects of silica and crushed sands (using different values of sand equivalent and passing No. 200 sieve) on water demands of mortar were investigated.

A strong correlation was found between the sand equivalent and fine materials passing No. 200 for silica sand, whereas there was no correlation for the crushed sand. This indicates that the amount of fine materials in silica sand can be determined by either passing No. 200 sieve or sand equivalent test. However, the sand equivalent test can be misleading in crushed sand. For the same workability, the results indicated that there was a direct relation between water demand and the amount of materials passing No. 200 sieve for both silica and crushed sands. However, there was a good correlation between water demand and sand equivalent for only silica sand.
Effect of Elastic Modulus of Capping Material on Measured Strength of High-Strength Concrete Cylinders
Authors: Vichit-Vadakan W , Carino NJ , Mullings GM
Published: January 2010

Studies have shown that end conditions of concrete cylinders tested in compression can have a significant effect on the measured strength of the cylinders, especially when high-strength concrete is used. The ASTM standard for bonded caps has requirements for minimum cube strength of the capping material and maximum cap thickness. However, a study by researchers at the National Ready Mixed Concrete Association (NRMCA) showed that the 50 mm cube strength may not be very useful in determining whether the capping material will perform adequately when testing high-strength concrete. In the study reported in this paper, the dynamic modulus of elasticity and modified cube strength (ASTM C 116) of various capping materials were evaluated as a function of age. The results showed that each capping material has a unique relationship between dynamic elastic modulus and cube strength. The elastic modulus of different capping materials can vary greatly at a given cube strength. For example, at a modified cube strength of 80 MPa, the elastic modulus of neat cement paste, at 30 GPa, was twice the elastic modulus of one sulfur mortar, at only 15 GPa. The elastic modulus of the capping materials was correlated with previously reported cylinder strengths. In cases where the cylinder strength was affected by the capping material, there is evidence that the cylinder strength was related to the modulus of elasticity and not to the cube strength of the capping material.
Two-Hour Zero Slump Loss, High-Strength Pumpable Concrete—An Application Case in Dam Structure
Authors: Feng N , Zhuang Q
Published: January 2010

About 700 000 m3 of pumpable concrete, which was produced by a high-range water-reducing admixture (HRWRA) and relatively low-strength cement, was used in the Xiao Lang Di water conservancy project. The concrete achieved a 28-day compressive strength as high as 90 MPa, a slump of 20 cm, and almost no slump loss in 2.5 h after mixing, as well as good freeze-thaw durability. The paper describes in detail the mix proportions, the method to control slump loss, and the related mechanical properties.