bluuebunny/crossref_metadata_2025 huggingface dataset:
Alkali Limits for Prevention of Alkali-Silica Reaction: A Brief Review of their Development
Authors: Hill ED
Published: January 2010

The optional limit on the Na2O equivalent of portland cement, 0.60% maximum, originated in the early 1940s following recognition of concrete distress caused by alkali-silica reaction by the California Division of Highways and the U.S. Bureau of Reclamation. Over the years, it has been effective in preventing distress from alkalisilica reaction in a great many, but not all cases. Aggregates have since been identified that require additional mitigating measures, such as inclusion of pozzolans. The need for different methods of aggregate evaluation has also been shown. Limits on the total alkali content of concrete have also been found useful. It is now apparent that a single alkali limit is impractical for all cases. The wide variety of natural aggregates requires that the cementitious materials be matched to the aggregates.

The intent of this paper is to present some of the highlights in the development of methods to avoid deleterious alkali-silica reaction. No attempt has been made to present a complete review.
Selectivity of Alkaline Activators for the Activation of Slags
Authors: Shi C , Day RL
Published: January 2010

Ground-granulated blast-furnace slag is being used increasingly as a replacement of portland cement in concrete. A review of literature and results from experimentation show that alkaline activators have selectivity; that is, different activators have variable activation effects on slags from different origins. Analysis of hydration chemistry indicates that the selectivity results from the variation of hydration products and microstructure from different combinations of slag and activator. Selectivity of activators suggests that strength of a blast-furnace slag with NaOH solution (ASTM C 1073) is better used as an internal quality control index rather than a quality evaluation index. To improve the sensitivity of the quality control test, the alkali may be selected based on an activator-optimization testing rather than specifying an alkali.
The Use of the Flow Length Concept to Assess the Efficiency of Air Entrainment with Regards to Frost Durability: Part II—Experimental Results
Authors: Pleau R , Pigeon M , Laurencot JL , Gagné R
Published: January 2010

Samples from 20 concrete mixtures were submitted to microscopical examination in order to record the size-distribution of the circles intercepted by a plane and the chords intercepted by a line of traverse. These data were used to determine the flow length and other characteristics of the air-void system by using a numerical method developed earlier. The flow lengths were correlated to the results obtained from freezing and thawing tests previously carried out on the same concrete mixtures. They were also compared to spacing factors and Philleo factors obtained from the same experimental data. The results of these correlations confirm the validity of the flow length concept and the numerical method used to calculate it. They clearly suggest that the flow length is a better indicator of the frost durability of concrete than the commonly used Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete (ASTM C 457) spacing factor, and more realistic indication of the actual spatial distribution of air voids in concrete than the Philleo factor.
Monitoring the Influence of Water and Ionic Ingress on Cover-Zone Concrete Subjected to Repeated Absorption
Authors: McCarter WJ
Published: January 2010

This paper presents data from a test program investigating water and ionic movement in the cover region of reinforced concrete under a cyclic wetting and drying regime. Experiments were conducted over an eighteen month period on slabs containing OPC and OPC with partial replacement with PFA and GGBS, with samples being exposed to water and chloride solution. Water and ionic ingress through the cover zone was monitored by means of small conductivity probes embedded within the surface of 50-mm concrete specimens. The conductivity profiles obtained from the experimental program highlight the influence of repeated absorption on water and ionic ingress, hydration, pozzolanic activity and chloride binding. A simple electrical model was used to explain the influence of pore fluid and microstructure on conductivity. Traditional methods of examination were also employed to corroborate conductivity data and included cumulative volumetric gain, coring for carbonation and chloride ingress, and drillings for chloride concentration profiles.
Test Method for the Potential Release of Hydrogen Gas from Silica Fume
Authors: Edwards-Lajnef M , Aïtcin P-C , Wenger F , Viers P , Galland J
Published: January 2010

Most silica fumes contain a small amount of silicon metal. Silicon reacts with alkali or alkaline-earth hydroxides when water is present to yield hydrogen. The reaction mechanism is similar to the one used to produce cellular concrete or expanding grout with aluminum powder.

There is concern that hydrogen release can cause problems when silica fume is used in grouting prestressing tendons because atomic hydrogen embrittles steel, thereby shortening the life of the prestressed concrete structure.

Moreover, if the partial pressure of hydrogen in air attains a certain level, there is a risk of explosion in the presence of a source of heat or spark. Portland cement-based materials with silica fume that contains some silicon do not present an induction period that could delay hydrogen release. Therefore, users of silica fume should be aware of this potential danger.

Because most users of portland cement are unfamiliar with techniques for measuring the silicon content of silica fume, a simple and rapid measurement method is shown here to evaluate the amount of hydrogen that can be released from a given silica fume. This value can be used to calculate the amount of silicon contained in the silica fume.
The Role for Fracture Mechanics in Reinforced Concrete Design
Authors: Hawkins NM
Published: January 2010

The performance under applied and environmental loads and the proportions selected for reinforced concrete members are determined primarily by two factors: the properties of the concrete used in those members and the mathematical models used to design those members. Standard tests such as cylinder compression, modulus of rupture, and splitting tension are now used to characterize the properties of the concrete for design and for quality control purposes. Yet those tests do not provide the information necessary to distinguish between the likely characteristics in practice of different high-performance concretes. Post-cracking behavior, which controls stiffness and durability at service loads especially for unidirectionally and lightly reinforced members, is closely tied to concrete properties (fracture softening) best established through displacement controlled fracture type tests.

Fracture mechanics concepts will not influence building code provisions for reinforced concrete until practitioners start using those concepts to improve their designs. To facilitate that action, efforts need to be concentrated on developing data that correlate the relative contributions of the fracture softening properties of different concretes to building code provisions that control designs in which only unidirectional reinforcement is desired. When that correlation has been established, and when appropriate fracture softening characteristics of different typical concretes have been determined through a comprehensive test program, then designers will need an ASTM Standard that they can use to check that, for the actual concrete placed in their structure, the fracture softening characteristics used in their design are being achieved.
Results of an Interlaboratory Test Program: Compressive Strength of Concrete
Authors: Kennedy S , Detwiler R , Bickley J , Thomas M
Published: January 2010

Although both ASTM and CSA have had standards for testing the compressive strength of concrete cylinders since the 1920s, neither standard contains a statement of the within- and between-laboratory precision of its test method as prescribed by Practice for use of the Terms Precision and Bias in ASTM Test Methods (ASTM E 177). This paper describes an interlaboratory study performed by 16 CSA-certified Ontario testing laboratories in accordance with Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method (ASTM E 691). The analysis shows that the variability of the test results increases with the mean strength of the concrete. A precision statement based on the results reported here is recommended for inclusion in Test Method for Compressive Strength of Cylindrical Concrete Specimens (ASTM C 39) and CSA A23.2-9C (Compressive Strength of Cylindrical Concrete Specimens).
Limitations of the Carbonate Extraction/UV Spectrophotometric Method for Determining Lignosulfonate-Based Admixtures in Hardened Concrete
Authors: Sanders CI , Sadeghi SS , Nelson NL
Published: January 2010

In 1963, a method for determining lignosulfonate addition rates in portland cements was reported (Wexler and Brako 1963). Over the years, this procedure has been adopted as the most common method for determining lignosulfonate-based admixtures in hardened concrete. The procedure involves extraction of lignosulfonate derivatives from pulverized concrete with an alkali-carbonate solution. The concentration of the extracted derivatives is then measured by comparing their ultraviolet (UV) spectra with those obtained from appropriate concrete standards.

While widely applicable, we have encountered numerous limitations when using this method to investigate concrete performance problems. Among the factors that may affect the results of the carbonate extraction/UV spectrophotometric procedure are the source of lignosulfonate in the admixture, cement content, concrete maturity, and certain extractable constituents such as other admixtures, cement additives, organics from fly ash, and unknown constituents. In this paper, we will discuss the results of systematic studies that have been performed to determine how each of these variables can influence the accuracy of results obtained.
Determination of a Nitrite-Based Corrosion Inhibitor in Plastic and Hardened Concrete
Authors: Jeknavorian AA , Chin D , Saidha L
Published: January 2010

The use of DCI® (W. R. Grace and Company, Cambridge, MA) corrosion inhibitor, a 30% solution of calcium nitrite, has become an established method for reducing the corrosive action of chloride on reinforcing steel in concrete. Certain regulatory agencies require monitoring the admixed concrete to verify that the specified amount of corrosion inhibitor has been added. This paper discusses a field test for confirming the presence of nitrite in plastic concrete and a laboratory method for measuring the addition rate of a nitrite-based corrosion inhibitor for hardened concrete. Our experience with these methods indicates that the concrete mix design does not generally affect the extraction of the nitrite from the concrete. However, to assure an accurate estimation of the admixed nitrite, where less than 85% recovery is achieved, the amount of nitrite extracted from the test sample should be compared to that of a reference concrete having the same mix design.
Determination of Blast-Furnace Slag Content in Hardened Concrete by Electrical Conductivity Methods
Authors: Xie P , Gu P , Fu Y , Beaudoin JJ
Published: January 2010

Electrical conductivity measurements were made on concrete systems containing blast-furnace slag. It was found that the slag content significantly influenced the concrete conductivity. A linear relationship between the concrete conductivity and the slag content and the volume fraction of aggregate was established by experiment. The relationship can be expressed as follows σc=ka·ϕa+ks·(slgc)+ko where σc is the concrete conductivity; φa is the volumetric fraction of aggregate; (slg/c) is the relative content of slag by weight of cementitious materials; and ka, ks, and ka are empirical coefficients. This relationship provides a basis for the determination of slag content in hardened concrete by electrical conductivity methods.
Factors Affecting the Durability of Concrete and the Benefits of Using Blast-Furnace Slag Cement
Authors: Idorn GM , Roy DM
Published: January 2010

Classical experience and research in the United States and Europe on the durability of concrete in marine environments are reviewed. Special precautions were recognized early as necessary for resisting the combined physicochemical effects of exposure to seawater. In the United States, quality work resulting in dense impervious concrete was an appropriate response while the use of blast-furnace slag cements met with favor in several European countries.

The durability of contemporary concrete is discussed in view of changed technology and performance requirements. Blast-furnace slag cements are found to provide desirable dense microstructures and chemical immunity to attack by sulfates and alkalies.

The implications for performance of concrete of heat development during curing are discussed as a new feature, less recognized in past technology. Application of supplementary testing is suggested, in particular isothermal and adiabatic calorimetry. The effective use of the heat of hydration and of blended cements could thus be assured.
Resistance to Freezing and Thawing of Silica Fume Concrete
Authors: Aïtcin P-C , Vezina D
Published: January 2010

The resistance to freezing and thawing of a concrete containing silica fume that was used during the construction of an experimental section on highway A25 in Montreal was done according to ASTM Test for Resistance of Concrete to Rapid Freezing and Thawing (C 666). The original mix was modified so that silica fume replaced three times its weight of cement.

The use of silica fume did not create any particular problems as far as the air content and slump were concerned except perhaps that slightly higher losses were observed during the transportation in comparison to the regular mix. The 28- and 91-day compressive strength results proved that silica fume has been more active than three times its cement weight.

The tests show that the resistance to freezing and thawing of the silica fume concrete was far superior to the plain concrete used for the completion of the project. The length increase and the absorption of the silica fume concrete were about or less than half of those observed with the regular mix. The durability factor of the silica fume concrete was 83 at the end of the test whereas the regular mix durability factor was only 68.
Effect of Fineness on Properties of Classified Cements
Authors: Kumar A , Roy DM
Published: January 2010

The effect of fineness of cement clinkers upon their early age hydration characteristics is presented. Class C (American Petroleum Institute [API] classification) or ASTM Type III portland cement was separated into three new fractions of varying surface area using an air classifier. Thermogravimetry, X-ray powder diffraction, and scanning electron microscopy were used to follow hydration in pastes up to 28 days. Microhardness measurements were also conducted. Mortars were used to follow compressive strength development up to 180 days.

Results indicate low surface area cements produce significantly lower strengths at early ages. Values of compressive strength for mortars made with cements having surface areas equal to or greater than 190 m2/kg (Blaine) reach comparable values in 90 days.
Correlation of Hardened Concrete Air-Void Parameters Obtained by Linear Traverse with Freeze-Thaw Durability as Found by ASTM C 666
Authors: Walker HN
Published: January 2010

The spacing factor for the proportional number of small air voids ¯Lps as proposed by Walker in 1980 and the air-void parameters normally obtained by ASTM Practice for Microscopical Determination of Air-Void Content and Parameters of the Air-Void System in Hardened Concrete (C 457) were each correlated with the durability factor and weight loss found by ASTM Test for Resistance of Concrete to Rapid Freezing and Thawing (C 666) Procedure A for 151 concretes. The correlation coefficients were examined, and it was found that for the durability factor the classical spacing factor from ASTM C 457 gave a slightly but not significantly better correlation than did ¯Lps. The 151 concretes were divided into three groups according to their source. In no case did the correlation obtained from ¯Lps significantly exceed the spacing factor calculated from ASTM C 457.
Measures of the Workability of Steel Fiber Reinforced Concrete and Their Precision
Authors: Johnston CD
Published: January 2010

Measurements of the workability of freshly mixed steel fiber reinforced concrete have been conducted using the traditional slump test, the British Standard V-B test and the test for time of flow through an inverted slump cone recently issued as ASTM Test Method for Time of Flow of Fiber Reinforced Concrete Through Inverted Slump Cone (C 995). Differences between the tests in terms of the extent to which they assess the stability, mobility, and compactability of fresh concrete are identified, and relationships between the results of each type of test are discussed in this context. The single-operator and between-operator precision of the results for each type of test are examined using four operators repeating each test three times on a total of 18 different mixtures with aggregate maximum size, fiber content, and fiber aspect ratio as the variables. Precision is analysed in terms of both standard deviation and coefficient of variation, and the dependence of each of these measures of precision on the magnitude of the mean is examined in terms of correlation coefficients. Using limits within which 90% of the 72 results for single-operator standard deviations fall, criteria suitable for precision statements are established for each of the three tests.
Studies of the Hydraulic Properties of Belite Middling Slime
Authors: Yanev I , Radenkova-Yaneva M
Published: January 2010

Hydraulic properties of belite middling slime obtained as a byproduct in the production of aluminum oxide from nonbauxite materials have been studied. For the purposes of the investigation belite slime and hydraulic lime were mixed in different proportions. Two types of admixtures were used, and their effect on the processes of hydration of the belite slime and strengths of the pastes with equal workability was studied. Development of the processes of hydration and strengths versus time of hydration was studied. By means of the scanning electron microscope, calcium-hydrosilicate phases were identified and a mechanism for their formation was proposed. The results obtained are discussed, and for the investigated binders suitable ranges of application are suggested.
Optimizing the Amount of Class C Fly Ash in Concrete Mixtures
Authors: Majko RM , Pistilli MF
Published: January 2010

This paper describes the results of a two part research program on several laboratory air-entrained concrete mixtures designed to contain increasing amounts of moderately cementitious Class C fly ash. In the first part of the paper, a Type A admixture was used in half of the mixtures, treating both the portland cement Type I and fly ash (15% calcium oxide). In the second part of the paper, three other Class C fly ashes (9 to 12% calcium oxide) were extensively tested in concrete that contained a Type A admixture (but this time treating only the cement). Two very high lime fly ashes (25 to 30% calcium oxide) were also tested in concrete mixtures.

All the fly ash concrete mixtures, provided they were properly air-entrained, showed excellent freeze-thaw durability (85 to 95% relative durability [RDF]) and good air-void parameters even at high fly ash contents. The setting times for the fly ash mixtures were longer by 4 to 6 h in the presence of a water reducer and very high fly ash contents (119 to 178 kg/m3 [200 to 300 lb/yd3]).

Also in Part 1, the optimal fly ash replacement (criteria is 28-day compressive strengths and 1:1 replacement basis) was 25% without a water reducer and >33% with a water reducer at 356-kg/m3 (600-lb/yd3) cementitious material. For 297-kg/m3 (500-lb/yd3) cementitious material, these values changed to 20% and >33%, respectively. Again using 28-day strengths and pound for pound replacement as the criteria, the optimal fly ash replacement at 356-kg/m3 (600-lb/yd3) cementitious material was >50% for Crawford fly ash, 33% for Will Co. fly ash, and 25% for Joliet fly ash. At 297-kg/m3 (500-lb/yd3) cementitious material, these optimum replacements were 25%, >40%, and slightly less than 20%, respectively.
Experimental Examination of Fly Ash Concrete
Authors: Marusin SL
Published: January 2010

Five mixtures were prepared from pure chemicals (tricalcium aluminate, calcium hydroxide, gypsum and 6% sulfurous acid) to examine the reactions of calcium sulfite with calcium aluminate by scanning electron microscope (SEM) procedures. Subsequently, two series of concrete mixes using the pozzolan cements were prepared: one to investigate the relative effects of calcium sulfite and calcium sulfate at constant calcium hydroxide and fly ash levels and the second to investigate the relative effects of sulfite and calcium hydroxide at a constant fly ash level. A comparison of effects of sulfite and sulfate and a comparison of calcium hydroxide and calcium sulfite were made using values of compressive strength and SEM analyses of the samples. Photomicrographs of microstructures and X-ray analyses were used to illustrate the findings.
Investigation of Cement for Concrete to be Used in Structures Near Seawater
Authors: Muravljov M , Jevtić D
Published: January 2010

The paper deals with experimental research concerning the use of cement with the addition of slag when preparing concrete with certain desired properties. Shown are results of experimental research using cement with the addition of 20% slag, crushed aggregate, water, and admixtures, and one high-range water reducer and one “water-proofer” in order to obtain water resistant concrete of high compactness and high strength. The concrete obtained satisfied the desired conditions, using the admixtures, having a low water cement ratio (W/C) but having very good workability. The second part of paper deals with the determination of cement resistance to aggressive water. Since a cement with a sufficiently low percentage of tricalcium aluminate necessary to be resistant to seawater is not always available, we suggest the use of concrete of the highest obtainable density. The coefficient of seawater resistance is obtained by comparing the flexural strength of specimens cured for six months in ordinary water and specimens cured in simulated seawater solution for the same period of time. A higher coefficient of resistance is obtained on specimens with a low W/C, using admixtures compared to those without admixtures, both being of the same consistency in spite of the usage of cement containing a higher percentage of tricalcium aluminate.
Diagnostic Monitoring of the Physio-Chemical Processes in Hydrating Cement Paste
Authors: McCarter WJ , Afshar AB
Published: January 2010

This paper details a novel electrical technique for monitoring the chemical and physical changes occurring within cement paste. The present study has concentrated on the initial 24 h after gaging with water and investigates the influence of retarders, accelerators, and cements of different type on electrical response. A microcomputer-controlled data acquisition system was developed to obtain results that can be used to obtain accurate electrical response/time curves. This is an advancement on earlier techniques. The work has correlated changes in electrical response with known chemical changes and structure building processes in cement paste. The method described also offers a technique for assessing the influence of chemical additives on the setting and hardening processes.
Effect of Rheological Properties of Cement Pastes on Workability of Mortars
Authors: Atzeni C , Massidda L , Sanna U
Published: January 2010

With a view to establishing a relationship between the rheological behavior of cement pastes with varying water/cement (W/C) ratios and the workability of different mortars, rotoviscosimetric (hysteresis cycle and transient) tests were conducted on the pastes, and slump and flow tests were performed on the mortars. Yield value was taken as the parameter representative of paste rheology. Because of the absence of a standardized slump test for mortars, a special truncated cone was designed. The τo values obtained in the rotoviscosimetric tests are represented as a function of the W/C ratio; and the slump and flow tests are represented as a function of the aggregate/cement (A/C) ratio.

The possibility of correlating τo of the pastes with the results of slump and flow tests conducted on mortars is then illustrated. A dimensionless parameter is proposed, which contains both the terms of mortar composition and the parameter τo of the pastes, with which workability measurements can be unequivocally correlated. By this means the workability of a mortar can be derived from the knowledge of the rheological properties of the paste of given composition used in its manufacture.

Finally, the advantage of introducing, in addition to the other elements characterizing the cement, a rheological factor for deriving the workability, however, expressed, is discussed.
Assessing Fire Damage of Concrete by the Ultrasonic Pulse Technique
Authors: Chung H-W , Law KS
Published: January 2010

When a concrete member is exposed to fire, the exterior of the member is heated up drastically, while the interior remains at a relatively low temperature. Only a thin surface layer of the concrete is subjected to severe damage. Knowledge of the extent of damage is most useful to the engineer in estimating the repair work. Thickness of the damaged layer can be expediently assessed by measuring the velocity of ultrasonic pulses along the surface. Accuracy of this technique has been investigated with a series of tests in which the concrete was heated to various temperatures. Test results indicate that the method of assessment is reasonably accurate. However, extensive cracking of concrete at very high temperatures may make the ultrasonic measurements very difficult and, hence, limits the applicability of the technique.
Mathematical Evaluation of the Quality of Repairs on Concrete Specimens
Authors: Kostrenčić Z , Bjegović D , Balabanić G
Published: January 2010

By comparing ultrasound pulse velocities before and after repairs on concrete and reinforced concrete structures, it is possible to assess the efficiency of repairs. Two statistical ways are shown in the paper: (1) comparing the velocities and using t-test (Student) and (2) using the x2-test. The former is good in application when individual repairs are considered, and the latter is good when a great number of repaired places is under consideration, and the success and the stability of the whole structure is assessed. The methods were applied on bridge prestressed beams and the advantages of each are shown in examples.
Corrosion of Reinforcing Steel in Concrete Containing Slag or Pozzolans
Authors: Maslehuddin M , Al-Mana AI , Saricimen H , Shamim M
Published: January 2010

Use of fly ash, silica fume, natural pozzolans, and blast-furnace slag in concrete is becoming increasingly common. Incorporation of these materials improves the durability of concrete. But as yet there are few quantitative data available on the effect of these materials on long-term corrosion of steel reinforcement. Such data will help the concrete technologists to select the proper type of materials to produce dense and impermeable concrete to withstand aggressive service environments.

In this investigation, the long-term corrosion-resisting characteristics of concretes made with two fly ashes, a natural pozzolan, a blast-furnace slag cement, and a preblended portland-fly ash cement were evaluated. Specimens were immersed in 5% sodium chloride solution for a period of more than five years, and the corrosion activity was evaluated by monitoring the half-cell potentials and measuring the corrosion rate of embedded steel using linear polarization resistance technique. Results indicate that addition of pozzolans or slag increases the corrosion-resisting characteristics of concrete. The corrosion rate of steel in concrete made with blast-furnace slag cement is lower than in other concretes.
Synergistic Roles of Slag and Silica Fume in Very High-Strength Concrete
Authors: Sarkar S , Aitcin P-C , Djellouli H
Published: January 2010

A very high-strength concrete (W/C = 0.20) containing 10% silica fume, 30% slag replacement for cement, and a high-range water-reducing admixture attained a compressive strength of 94 MPa at 28 days. The microstructural development of this concrete was studied from 1 to 28 days with SEM/EDXA and TEM. The slag used was reactive, with 70% melilite group phases and an index of hydraulicity of 1.2. Microstructural changes occurring in the first 28 days are presented. The factors responsible for promoting strength are also discussed.
Molybdenum Trioxide—An Accelerator of Portland Cement Hydration
Authors: Fischer HC
Published: January 2010

Technical-grade molybdenum trioxide (MoO3) significantly accelerated the hydration of portland cement at 5 to 10% (by weight of cement) dosages. This somewhat unusual reactivity was observed and qualitatively measured via calorimetry.
Comparison of Slump Cone and V-B Tests as Measures of Workability for Fiber-Reinforced and Plain Concrete
Authors: Balaguru P , Ramakrishnan V
Published: January 2010

In this paper, two popular measures of workability, namely, slump and V-B time, are compared for plain and steel (hooked) fiber-reinforced concrete. The results are based on experiments made on both types of concrete with and without high-range, water-reducing admixture. The fibers were 50 mm (2 in.) long with deformed ends glued together side by side into bundles (collated) with a water-soluble glue. The W-C ratio varied from 0.3 to 0.62. The air content ranged from 2 to 12%. In terms of workability, the whole spectrum ranging from no slump concrete to flowing concrete was covered.

Based on the results of this investigation, the following general equation can be written relating V-B time and slump log10(V∙B)=a−b(slump)

The addition of high-range water reducer and fibers influences the relationship and hence the constants a and b. The slope of the line, b, is highest for plain concrete without high-range, water-reducing admixture and lowest for fiber-reinforced concrete. In the case of plain concrete, the addition of high-range water reducer seems to result in a more cohesive mixture. As a result, V-B times can be recorded for slumps as high as 163 mm (6.4 in.). Without the addition of the admixture, concrete seems to collapse around a slump of 89 mm (3.5 in.). The addition of fibers increases the cohesiveness of the mixture considerably. For fiber-reinforced concrete made using high-range water reducer, V-B time could be measured for slumps as high as 221 mm (8.7 in.). Generally for a given slump, fiber-reinforced concrete has a higher V-B time than plain concretes.
A Systematic Method to Determine Optimal Specimen Geometry for Measuring Concrete Fracture Properties by the Peak-Load Method
Authors: Yang S , Tang T
Published: January 2010

The peak-load method is a simple method for determining the fracture properties KIcS and CTODc of the two-parameter fracture model of concrete. With this method, the fracture properties can be determined from the measured peak loads of several different (or distinct) specimens. Specimens can be made distinct in specimen shape, size, notch length, and loading configuration. To quantitatively identify the degree of specimen distinction, a variable named specimen distinction number is proposed. When test specimens are considerably distinct, random experimental errors have negligible effect, and determination KIcS and CTODc is of high accuracy. Thus test specimens can be optimized to obtain the most accurate values of the fracture properties. A previous experimental program found that change in specimen shape (e.g., a hole drilled at the axis of splitting tension cylinder) can largely expand the specimen distinction. An experimental program reported in this paper shows that changing loading configurations of beams (or prisms) from bending to eccentric compression can also largely enhance the specimen distinction and therefore provide KIcS and CTODc determination of high accuracy.
Multi-Laboratory Study of the Accelerated Mortar Bar Test (ASTM C 1260) for Alkali-Silica Reaction
Authors: Rogers CA
Published: January 2010

The accelerated mortar bar test, developed by the National Building Research Institute (NBRI) in South Africa, has been adopted in North America for the rapid identification of potentially alkali-silica reactive aggregates and may also be used for assessing the effectiveness of supplementary cementing materials. The purpose of the multi-laboratory studies, involving 46 and 32 laboratories, was to obtain data to develop a multi-laboratory precision statement for the test. The aggregates used in this study were Spratt siliceous limestone from a quarry in Ottawa, and a natural glacio-fluvial sand from north of Toronto in Ontario.

The natural sand gave an average expansion of 0.164% at 14 days and the quarried stone gave an average expansion of 0.417%. The multi-laboratory standard deviation after removal of outliers was found to be proportional to the amount of expansion. The average coefficient of variation at 14 days was found to be about 15% in the two studies.

The use of a single cement by all laboratories did not give a major improvement in precision. Autoclave expansion, and the alkali, sulfate and magnesium oxide (MgO) contents of cement were not related to mortar bar expansion at 80°C. A relationship was found between MgO content and autoclave expansion.

It is possible to prepare a precision statement as follows: For mortars giving average expansions after 14 days in solution of greater than 0.1% the multi-laboratory coefficient of variation (1s% of ASTM C 670) has been found to be 15.2%. Therefore, the results of two properly conducted tests in different laboratories on specimens of a sample of aggregate should not differ by more than 43% (d2s% of ASTM C 670) of the mean expansion.
Relationship Between Gas Adsorption and the Shrinkage and Creep of Recycled Aggregate Concrete
Authors: Gómez-Soberón JMV
Published: January 2010

In this work, an experimental analysis is described of specimens of recycled concrete (RC) made with replacement of natural aggregate with recycled aggregate originating from concrete (RCA). An experimental analysis to obtain the shrinkage and creep properties (basic and by drying) of RC was performed. The replacement fraction of natural aggregate with RCA were 0 %, 15 %, 30 %, 60 % and 100 % and the test conditions were 50 % RH and 20 °C. The results of these trials were compared with mercury intrusion porosimetry (MIP) and gas adsorption (nitrogen) tests, at 90 days. In the results, an increase in the shrinkage and creep properties of the RC with respect to conventional concrete was observed, while porosity values increased. However, the deformation evolution over time is similar to conventional concrete.
Crack Offset Corrections to Post-crack Performance Parameters Obtained from Third-point Loaded Fiber Reinforced Shotcrete Beams
Authors: Bernard ES , Tutlu E , Diamant1idis D
Published: January 2010

Fiber Reinforced Shotcrete (FRS) is used as an economically competitive method of ground support in tunnel excavations throughout the world. Fibres are incorporated into this material to impart post-crack load capacity. Beam tests are commonly used to assess the post-crack performance of FRS but high within-set variability has hindered the usefulness of beam test data. A method of correcting performance data to account for the offset between the position of the crack and the center of the beam has been suggested as a means of improving within-batch variability for post-crack performance parameters obtained from third-point loaded beam tests. In this paper, an offset correction method has been applied to a large set of beam test data obtained as part of Quality Control testing for a tunnel-lining project to determine whether the method is effective in reducing within-batch variability.
Simple Field Tests to Characterize Fluidity and Washout Resistance of Structural Cement Grout
Authors: Khayat KH , Yahia A
Published: January 2010

The ability to assess rheological properties of neat cement grout, such as those used in structural repair and for filling post-tension ducts, is of special interest for the evaluation of the ease of pumping, spreading into place, and filling of narrow spaces. There is an increasing need to identify dependable and simple test methods that can characterize the consistency of specialty cement grouts and reflect variations in rheological properties during handling and placement. Several tests can be used to evaluate the rheological characteristics of a cement grout suspension, including precise methods for the determination of rheological parameters and simple procedures to assess fluidity. Rheological properties can be accurately determined by using a coaxial cylinder viscometer. However, the use of such a viscometer is mainly limited to the laboratory, and simple methods including the mini-slump spread and the modified Marsh cone tests are usually employed in the field to verify the consistency for quality control.

This paper attempts to establish relationships between rheological parameters and fluidity values obtained using simple test methods. Relationships are also determined between the wash-out resistance of structural cement grout and various fluidity and rheological parameters. The derived relationships are based on a wide variety of cement grouts covering up to 210 data points. The various grouts were prepared with W/C ranging between 0.30 and 0.50, Type I and III portland cements, as well as various silica fume replacement values (up to 8% by mass), blast-furnace slag contents of 20 to 60%, fly ash substitutions of 10 to 30%, and limestone filler replacements of up to 30%. The investigated grouts incorporated melamine- and naphthalene-based high-range water reducer, welan gum and cellulose-based viscosity-modifying admixtures, as well as set-retarding admixture.

Test results highlight the difficulties of relying on a single empirical test to evaluate the fluidity of a given grout. Correlations between various simple measurements of fluidity and wash-out mass loss and apparent viscosities determined at different shear rates indicate that the mini-slump and wash-out mass loss measurements correspond well to viscosities determined at low-shear rates (5.1 s-1). In contrast, the modified Marsh cone measurement corresponds well to viscosity determined at high-shear rates ranging between 340 and 510 s-1. Because of the pseudo-plastic behavior of structural cement grouts, field quality control tests should include fluidity assessment at low and high shear rates to adequately evaluate the rheological behavior of the grouts.
Effect of Thermal Variations on Bond Strength of Fusion-Bonded Epoxy-Coated Bars
Authors: Elleithy WM , Al-Amoudi OSB , Sharif AM , Maslehuddin M
Published: January 2010

Fusion-bonded epoxy coating is extensively used to enhance the corrosion resistance of reinforcing steel. The bond strength between these bars and the concrete is expected to be less than that of the uncoated bars and it may be further impaired due to prolonged exposure to thermal variations. This investigation was conducted to evaluate the effect of thermal variations, simulating the changes in the night to day temperature, on the bond strength of fusion-bonded epoxy-coated steel reinforcement. The pull-out specimens, prepared using bars of two different sizes and two coating thickness, were exposed to thermal cycling. The critical and ultimate bond strength of the fusion-bonded epoxy-coated bars were compared with that of the uncoated bars. The results indicated a reduction in the critical bond strength between concrete and the fusion-bonded coated bars. Furthermore, the difference between the critical bond strength in the coated and uncoated bars decreased with increasing thermal cycles, indicating that thermal variation has a greater effect on bond strength than the coating thickness.
Expansion of Cements: Cause and Control
Authors: Hauser K
Published: January 2010

PCA Research Bulletin 45 concludes with 14 major points related to the effects of periclase, free lime, and C3A on “Hydration Expansion Characteristics” (the bulletin title), but it does not address the easy remedy available for those plants with inherently high MgO.

This paper discusses one practical solution, developed decades ago for a plant without the option of avoiding high MgO levels in the quarry, as well as a control procedure that will help avoid over-doing the chemical modification required and contribute to better uniformity.
The Permeability of Cement Systems to Chloride Ingress and Related Test Methods
Authors: Liu Z , Beaudoin JJ
Published: January 2010

The rapid chloride permeability test (AASHTO T277/ASTM C 1202) and other chloride permeability testing methods are critically reviewed. The basic concepts of concrete permeability and conductivity are also discussed. An attempt at clarification and resolution of some issues is made. A faster and simpler alternative testing method to the AASHTO T277/ASTM C 1202 based on the a-c impedance techniques is proposed. It provides at least an equivalent indication of the concrete permeability with respect to AASHTO T277/ASTM C 1202 and is without several shortcomings characteristic of the current methods.
Introduction to the Symposium on Developments in Test Methods for Alkali-Silica Reaction
Authors: Lane DS , Lobo C
Published: January 2010

The following papers in this issue were presented at an ASTM Committees C01 and C09 Symposium on Developments in Test Methods for Alkali-Silica Reaction held in December 1998 in Nashville. The symposium was organized at the suggestion of Leslie J. Struble, chairman of Subcommittee C09.26, Chemical Reactions.
Limits on Alkali Content in Cement—Results from a Field Study
Authors: Leming ML , Nguyen BQ
Published: January 2010

ASTM C 150 has optional limits on the equivalent alkalies in portland cement expressed as %Na2O + 0.658 × %K2O), often referred to as “Na2Oeq” where alkali silica reactivity is a potential problem. The prescribed limit of 0.6% by mass of the cement, which was developed over 40 years ago, has been questioned as not being sufficiently restrictive in some circumstances.

A 17-year-old bridge showing strong evidence of alkali-silica reactivity was studied as part of a larger investigation for the North Carolina Department of Transportation. The extent of noticeable map cracking was significantly different in different parts of the bridge. The differences could not be explained in terms of exposure to moisture or other environmental effects. Available information indicated that two different cements, with different alkali contents, were probably used at different times during construction.

Cores were removed from areas with obvious differences in cracking. All of the cores contained a reactive phyllite coarse aggregate. The alkali content was determined from selected cores. In addition, the area of material that fluoresced under ultraviolet light after treatment with uranyl acetate was determined on cores that had been split longitudinally. These factors were compared to the extent of cracking. No deleterious ASR was generated when the water-sol-uble alkali content was less than 1.5 kg/m3, or 0.55% by mass of the portland cement (Na2Oeq) with the reactive phyllite, at least for concrete in service for 17 years. A higher alkali content resulted cracking due to ASR.
Proposed New Test Procedure for Measuring Alkali-Silica Expansion Produced by Hydraulic Cement
Authors: Struble LJ , Pade C
Published: January 2010

Although there are several standard tests for measuring alkali-silica expansion produced by an aggregate, there is only one test suitable for measuring expansion produced by the cementitious material (C 441, Standard Test Method for Effectiveness of Mineral Admixtures of Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction). This mortar test uses Pyrex glass as the standard reactive aggregate. A new test has been developed to overcome these deficiencies. Also a mortar test, it utilizes Vycor glass rather than Pyrex glass and a procedure that does not produce condensation on the bars, which causes leaching of alkalies from the mortar. The test has recently been adopted by ASTM as a provisional standard to determine whether hydraulic cement produces deleterious expansion when combined with alkali-reactive aggregate in concrete.
Field Study of the Setting Behavior of Fresh Concrete
Authors: Abel JD , Hover KC
Published: January 2010

A simple test is introduced for monitoring setting behavior of concrete in the field. The method was inspired by the ASTM C 403 penetration resistance method for mortar setting time, coupled with the recommendation of ACI Committee 302 (Concrete Floors) that bull-floated flatwork surfaces are ready for subsequent finishing operations when a worker standing on the fresh concrete leaves a boot print about 6 mm (¼ in.) deep. In the proposed test a penetrometer probe was fabricated with a contact area approximately equal to the contact area under an adult-sized work boot. Setting is monitored by measuring the pressure required to embed the probe into the concrete surface to a depth of 6 mm (¼ in.). The method was used during construction of a pedestrian mall, and the results provide insight into the nature and variability of the setting behavior of concrete, and on the relationship between setting of concrete and the setting of mortar.
Specimen and Aggregate Size Effect on Concrete Compressive Strength
Authors: Issa SA , Islam MdS , Issa MA , Yousif AA , Issa MA
Published: January 2010

Test results obtained on the effect of specimen size and aggregate size on concrete compressive strength and modulus of elasticity are presented. The concrete was prepared using 4.75, 9.5, 19.0, 37.5, and 75-mm nominal maximum size aggregate. Over 600 cylinders were cast and tested for concrete compressive strength and modulus of elasticity. Four different sizes of plastic cylinder molds were used: 150 by 300 mm, 100 by 200 mm, 75 by 150 mm, and 50 by 100 mm. The testing was carried out in accordance with ASTM standards for concrete compressive strength (ASTM 39) and modulus of elasticity (ASTM C 469).

The test results were presented in terms of the concrete modulus of elasticity-to-compressive strength ratio (E/f′c) versus cylinder diameter, maximum aggregate size, age at testing, among other factors. The results revealed that a size effect exists. The strength ratio was higher for the larger nominal maximum aggregate size concrete at each testing date. Hence, as the nominal maximum aggregate size decreased, the strength ratio decreased. The strength ratio followed a dished trend with respect to specimen size. For each cylinder size, as the nominal maximum aggregate size increased, the coefficient of variation increased. It was also found that for the same nominal maximum aggregate size specimens, the coefficient of variation increased as the cylinder size decreased.