bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified Slump Test to Measure Rheological Parameters of Fresh Concrete
Authors: Ferraris CF , de Larrard F
Published: January 2010

The ease of placement of concrete depends upon at least two physical properties, the yield stress and plastic viscosity. Currently the most common field test is the slump test, and it is related only to the yield stress. Therefore, a simple field test method intended to provide an evaluation of the two Bingham rheological parameters, yield stress and plastic viscosity, was developed. To determine the plastic viscosity the time necessary for the upper surface of the concrete in the standard slump cone to slump 100 mm was measured. The apparatus and test procedure are described. Semi-empirical models are proposed for the yield stress and for the plastic viscosity as function of the final slump and slumping time. The application of the modified slump test for the evaluation of the viscosity is limited to concretes with a slump of 120 to 260 mm. If the validity of this test is confirmed in the future, it could be used as a field quality control test.
Effects of Superplasticizer, Retarding Agent, and Silica Fume on the Air Permeability of High-Performance Concrete
Authors: Gagné R , Ollivier J-P , Latreille Y
Published: January 2010

The aim of this research is to evaluate how transport properties at the surface and in the core of high-performance concrete (HPC) slabs are affected by silica fume and by superplasticizer and retarding agent dosages. The transport properties were evaluated by measuring the air permeability at two depths under the surface finished with a wooden trowel. The experimental program is based on eight different high-performance concrete mixtures (77 to 93 MPa) made with a water-to-binder ratio of 0.30. An ordinary portland cement (OPC) and a blended silica-fume cement (SF) were used to compare the effect of silica fume on the air permeability of surface and core concrete. Four mixtures were produced with a retarding agent to assess the effect of set retardation on the surface properties of high-performance concrete. For each combination of cement type and retarding agent dosages, the superplasticizer dosage was selected to produce two slump levels of 100 ± 10 mm and 200 ± 20 mm.

It was found that the air permeability of the concrete located just beneath the surface of HPC slabs can be 2 to 20 times higher than the core permeability. The ratio between the surface and core permeabilities depends on mix-design parameters such as silica fume, superplasticizer (slump), and retarding agent dosages. Increasing the slump of HPC (from 100 to 200 mm) systematically increased the surface permeability. The effect of slump (or superplasticizer dosage) on the surface permeability of the HPC decreased as compressive strength increased. The use of a retarding agent in HPC without silica fume increased the air permeability of the surface concrete. This effect is particularly important for the concrete containing a high dosage of superplasticizer. Silica fume proved very effective in inhibiting increased surface permeability due to the dosages of superplasticizers and retarding agents.
A Statistical Analysis of Hot and Warm Accelerated Concrete Curing Methods
Authors: Meyer D
Published: January 2010

Strength test results for accelerated-cured specimens, obtained after only 24 h, are used to predict the 28 day strength of concrete. Various accelerated curing methods are available. Two of these methods are compared in relation to the uncertainty of their predictions and the stability of the relationship between their 24 h and 28 day concrete strength. The results suggest that warm water accelerated curing is preferable to hot water accelerated curing of concrete. Various methods for reducing the uncertainty associated with the estimates of 28 day strengths are suggested. In particular it is suggested that the effect of variations in cement chemistry over time be addressed by using dynamic linear models with coefficients that vary over time.
Ultrasonic Testing to Determine Water-Cement Ratio for Freshly Mixed Concrete
Authors: Popovics S , Popovics JS
Published: January 2010

The objective of the research presented here was to find promising directions for the development of ultrasonic test method(s) for the direct, instantaneous determination of the water-cement ratio (W/C) in fresh mortar or concrete. The importance of W/C is related to potential strength development and, to a certain extent, the durability potential of the hardened concrete. Since previous efforts during the past 50 years have been unsuccessful in testing fresh concrete due to the complexity of the problem, innovative, high-risk/high-gain methods were selected in the present work. The methods are considered innovative since a literature search detected no sign that they have been used for testing fresh concrete before.

The following test methods were tried out for testing fresh concrete: • ultrasonic methods used regularly for testing hardened concrete; • solidification of the fresh mixtures by freezing or heat treatment or accelerating admixture + heat treatment before testing; • use of high-intensity stress waves by lithotripter; • the direct contact method.

None of these methods produced a satisfactory solution for the instantaneous determination of the water-cement ratio, although interesting side results were obtained. It is hoped that both the positive and negative results presented will help researchers in their work on ultrasonic testing of concrete.
Rheology of Cement Paste and Concrete
Authors: Struble L , Szecsy R , Lei W-G , Sun G-K
Published: January 2010

Much has been learned in recent years about the rheology of cement paste and how it relates to microstructure. Such progress has been made possible in part by the use of specialized instruments for measuring dynamic rheological properties, developed to characterize viscoelastic materials. This paper reviews recent studies of cement paste in our laboratory in which dynamic rheological properties are used to follow the effects of cement hydration. Not as much has been learned about the rheology of concrete. Measuring flow behavior of concrete presents interesting challenges; concrete rheometers have been developed, but they are not widely used. It appears likely that concrete rheology is controlled by rheology of its paste, although such links have not yet been directly established. This paper also presents preliminary results from our laboratory on concrete flow behavior. Concrete rheology provides important information about its workability, and rheological parameters have important advantages over slump when characterizing workability.
A New Test Method for Fiber-Reinforced Concrete
Authors: Zollo RF , Hays CD , Zellers R
Published: January 2010

It has long been recognized that the principal benefit gained by using fiber reinforcement in portland cement concrete is a conversion of the material from brittle to relatively ductile behavior. The apparent ductility, or toughness, is primarily related to the improved tensile strength of fiber-reinforced concrete (FRC) especially and even after significant matrix cracking has occurred. However, the methods used to measure tensile strength and toughness of FRC have been, at best, elaborate and controversial.

A practical and much needed testing methodology for fiber-reinforced concrete has been developed and adopted as an ASTM standard. It was conceived from the need to have a test that is relatively simple and inexpensive to conduct and is yet capable of assessing the tensile strength of cracked FRC. The test method, ASTM C 1399, and an interlaboratory testing program conducted to help formulate a precision statement for the new methodology is discussed.
Mechanical Properties and Freezing and Thawing Durability of Polypropylene Fiber-Reinforced Shotcrete Incorporating Silica Fume and High Volumes of Fly Ash
Authors: Zhang MH , Mirza J , Malhotra VM
Published: January 2010

This paper describes the materials used, mixture proportions, mixing and shotcreting operation, and properties of the fresh and hardened polypropylene fiber-reinforced shotcrete incorporating silica fume and high volumes of fly ash. The polypropylene fiber-reinforced high-volume fly ash shotcrete produced had satisfactory workability, mechanical properties, and resistance to freezing and thawing cycling. The shotcrete containing silica fume had negligible rebound compared with that without silica fume. The incorporation of fly ash and silica fume improved the workability of the fresh shotcrete, and this resulted in lower operating pressure for the shotcreting. The use of polypropylene fibers up to 0.5% by the volume of the shotcrete did not affect significantly the compressive strength, and the shotcrete incorporating both fly ash and silica fume bonded well to the base concrete. The fiber-reinforced shotcrete showed satisfactory performance after 300 cycles of freezing and thawing with a durability factor >80 even though the air contents were relatively low, and the spacing factor L¯ was relatively high.
Evaluation of the Effect of Portland Cement Alkali Content, Fly Ash, Ground Slag, and Silica Fume on Alkali-Silica Reactivity
Authors: Lane DS , Ozyildirum HC
Published: January 2010

The effects of portland cement alkali content, and replacement of portland cement with Class F fly ash, slag, or silica fume on alkali-silica reactivity (ASR) were studied by measuring the expansion of mortar bars made with Pyrex glass and stored over water at 38°C. Expansions were negligible with portland cements having alkali contents of 0.40% Na2O equivalent or less. Above 0.40%, expansions of bars made with cement only expanded linearly with cement alkali content after 56 days in storage through 336 days. Regression analysis yielded correlation coefficients of 0.91 for the 56 and 336 day expansions. An expansion of 0.10% was established as the maximum expansion indicative of a mixture providing acceptable mitigation of ASR.

The replacement of cement having alkali content of 0.50% and above with pozzolan or slag was found to reduce expansion. A procedure for normalizing the expansions of pozzolan and slag batches to the regression of cement control batch expansions is presented that allows comparison between batches on an equivalent basis by factoring out inherent testing variability. The level of expansion achieved was related to the alkali content of the cement and the type and amount of mineral admixture or slag used. The materials tested, several Class F fly ashes, a slag, and a silica fume were effective in preventing expansions when used in appropriate amounts with respect to the alkali content of the cement used. The mitigation provided by the materials tested was greater than would have been achieved through simple alkali dilution. Preventive methods based on total cementitious alkali content discount the effectiveness of Class F fly ash, slag, and silica fume in mitigating ASR.
Comparison of Field Observations with Laboratory Test Results on Concretes Undergoing Alkali-Silica Reaction
Authors: Whiting NM
Published: January 2010

Alkali-silica reactivity (ASR) was identified as contributing to premature failure of 12 concrete pavements in Minnesota. The available aggregate sources used in these distressed pavements were tested for potential ASR. Standardized tests result in conflicting information. The sands tested as potentially deleteriously expansive in the ASTM C 1260 Mortar Bar Test (expansion >0.2%), but tested as not deleteriously reactive in the ASTM C 1293 Concrete Prism Test (0.0295 to 0.042% expansions). Although expansions of these C 1293 prisms remained low, sand-sized opaline shales reacted to form gel, spalls, and cracks. Similar cracking and gel deposits are associated with these shales in field samples. The C 1260 mortar bars made with crushed quartzite aggregates exhibited moderate expansion values (average expansions ranging from 0.135 to 0.188%), but the C 1293 prisms made with quartzite coarse aggregates exceeded the 0.04% expansion limit (0.082 to 0.1137% expansion). Quartzite is reacting in several pavements but not as extensively as the high C 1293 test results imply. The sands are reacting in pavements and in test samples, but this reaction is not manifested as expansion in the C 1293 prisms.
Comparison of Results from C 441 and C 1293 with Implications for Establishing Criteria for ASR-Resistant Concrete
Authors: Lane DS
Published: January 2010

Several test methods are available to evaluate the potential susceptibility of concrete-making materials to deleterious alkali-silica reactions (ASR). These methods vary in the approaches they use to accelerate the reaction; acceleration being necessary to provide timely evaluations of materials in predicting long-term performance. As a consequence, the tests are not universally applicable, nor do they necessarily provide straightforward, consistent results using established criteria. This paper compares results of C 441 and C 1293 tests in an effort to develop specification criteria for ASR-resistant concrete.

ASTM C 441 uses Pyrex glass aggregate in mortars to accelerate the testing and provides reliable results in 2 months. It can be used to evaluate the effectiveness of pozzolans and ground slag to prevent expansions, as well as the effect of portland cements on the reaction. However, differences in the relative reactivity of Pyrex glass and the aggregates used in concrete construction should be considered in the engineering decision-making process. The C 1293 test has the advantage of testing the natural aggregates available for use in construction and achieves acceleration by artificially raising the alkali content of the concrete. Its disadvantages are that it takes at least 1 to 2 years for results, and cannot be used to evaluate the effectiveness of portland cements in resisting ASR.

C 1293 results can be considered to have more relevance to actual field constructions than results from C 441 tests because it tests construction aggregates. However, the 1 to 2 year testing period makes it impractical for general specification purposes. This paper illustrates the use of C 1293 results to determine which cementitious materials are effective in controlling the reactivity of a particular aggregate, coupled with C 441 testing of those same materials to establish an expansion limit in C 441 tests. The limit established for C 441 tests provides for timely testing that should be applicable to common hydraulic cementitious materials.
Using Accelerated Test Methods to Specify Admixtures to Mitigate Alkali-Silica Reactivity
Authors: Barringer WL
Published: January 2010

The development of accelerated tests for alkali-silica reactivity (ASR) included the investigation of a wide range of aggregates and cements that gave results indicating the potential reactivity of these combinations. The development procedure did not provide for comparison of specific aggregates and cements in areas where ASR is known to be of concern. Through the development of a matrix comparing available materials and their reactions, specifications for concrete proportions may be developed to further alleviate the effects of ASR in a specific area. Tests conducted, using New Mexico aggregates and available admixtures in conjunction with AASHTO Test Method T 303, indicated that fly ash and fly ash/lithium admixtures resulted in significant reduction in expansion of mortar bars.

The matrix for this research involved five fly ash sources, five aggregate sources, one local cement, and a lithium nitrate solution.

Subsequent to this research, the New Mexico State Highway and Transportation Department has implemented the findings into their specifications for infrastructure concrete.
Evaluation of Laboratory Test Methods for Alkali-Silica Reactivity
Authors: Fournier B , Malhotra VM
Published: January 2010

In 1991, the Canada Centre for Mineral and Energy Technology (CANMET) initiated a major research project dealing with preventive measures against alkali-silica reaction (ASR) in concrete. The main objective of the above project is to develop a comparative field and laboratory engineering database on the longterm effectiveness of supplementary cementing materials (SCMs) in controlling and/or reducing expansion and cracking in concrete due to ASR. The results obtained to date indicate that the effectiveness of SCMs in controlling expansion due to ASR is a function of various parameters such as the composition and proportion of the different types of SCMs in concrete (for example, fly ash, slag, silica fume), the total cementitious materials and/or total alkali content in the system, and the reactivity level of the aggregate. Accelerated concrete prism and mortar bar expansion test methods can be used in the laboratory to predict the long-term performance of SCMs in controlling expansion due to ASR.
Anhydrite in High Sulfur Trioxide (SO3)/Alkali Clinkers: Dissolution Kinetics and Influence on Concrete Durability
Authors: Michaud V , Suderman RW
Published: January 2010

Changes in the cement manufacturing process, such as the use of higher sulfur fuels, have tended to raise clinker sulfate levels and sulfur trioxide (SO3) alkali ratios. As one of the consequences, the nature and quantity of the clinker sulfate phases have been modified. Clinker sulfates tend to be available as double sulfate salts; calcium langbeinite instead of potassium sulfate.

Anhydrite is present in the clinker only when the quantity of clinker sulfate is higher than the amount that can be combined by the alkali ions as alkali sulfates and calcium langbeinite. It has been demonstrated recently that in clinkers with sulfate/alkali ratios as high as 3.6, anhydrite is not detectable and only begins to form at levels above this. This is consistent with observations from regular industrial production. Even with fairly high sulfate levels and SO3/alkali ratios, industrial clinkers do not attain high enough SO3/alkali ratios to permit anhydrite formation. Thus, the presence of clinker anhydrite is illusive.

It has been alleged recently that clinker anhydrite would provide nonheat-cured concrete with a lesser durability. The objective of this study is to establish what would be the effect of anhydrite on durability in the hypothetical case that this phase was present in clinker. The impact of clinker anhydrite has been examined on a laboratory clinker with a SO3/K2O ratio of 5.2 and a SO3 level of 3.8%. The laboratory clinker anhydrite amount has been evaluated at 1.1%. Two aspects have been studied: • The dissolution rate of clinker anhydrite present in a very high SO3/alkali clinker during hydration, and • The influence of clinker anhydrite on expansion.

Experiments indicate that anhydrite dissolves and reacts quite quickly, mainly within a few days, and does not produce concrete with expansion. Therefore, clinker anhydrite, if it did exist, would not contribute to ambient temperature DEF.
Delayed Ettringite Formation (DEF) in Structural Lightweight Aggregate Concrete: Effect of Curing Temperature, Moisture, and Silica Fume Content
Authors: Rønne M , Hammer TA
Published: January 2010

The results confirm that the self-desiccation of normal density (ND) high strength concrete may prevent delayed ettringite formation (DEF). However, when using lightweight aggregate (LWA), the initial water content of the LWA grains seems to be sufficient to give some DEF. The results also confirm that the critical temperature, provided that the moisture content is sufficiently high, is in the range of 65 to 70°C for ND concrete with Norwegian cements. The critical temperature for LWA concrete seems to be somewhat higher; above 70°C. The LWA expansion due to DEF seems to be somewhat lower than the expansion of ND concrete, provided they have the same binder and paste quality. The volume increase coincides with an extensive compressive strength reduction. The reported results confirm that addition of silica fume (5%) in combination with the investigated cements, seems to prevent or eliminate the DEF.
Assessing the Distribution of Sulfate in Portland Cement and Clinker and Its Influence on Expansion in Mortar
Authors: Tennis PD , Bhattacharja S , Klemm WA , Miller FM
Published: January 2010

The present work is a continuation of a study previously reported on the characterization and analysis of 33 different clinkers from North American cement plants which varied widely in molar SO3/Na2Oeq, SO3 content, and mineralogical phase distribution. This research examined the distribution of sulfur in a broad range of clinkers and identified its presence as alkali sulfates, alkali calcium sulfates, and as sulfate incorporated in the silicate phases. As a key part of the work, it has been necessary to develop relevant analytical methods for measuring potentially slowly soluble sulfate in clinker phases. The selective dissolution procedures described are applicable to the evaluation of sulfate distribution of both clinker and finished portland cement.

In the current phase of the study, physical measurements are being performed to substantiate the chemical observations of the earlier work. Five cements commercially ground from clinkers characterized earlier were chosen for further evaluation based on various sulfate levels and sulfate/alkali ratios. The volume stabilities of mortar bars (25 by 25 by 255 mm) made with these five cements were determined for several curing conditions: curing and storage under water at 23°C; curing for 24 h at 23°C, with subsequent storage under water at 38°C; 4 h initial curing at 23°C, followed by a 12-h exposure to 70 or 80°C, followed by storage under water at 23°C. The rate of temperature increase or decrease was 20°C/h in all cases. These mortar bars were prepared according to European Standard EN 196-1 with German DIN Standard Sand (Normensand). After 28 weeks of storage, bars appear to have stabilized below about 0.03% expansion. More recent testing has begun using mortar bars prepared with the above cements plus two additional Type III cements commercially ground from two of the same clinkers. These mortars have been prepared with an ASTM C 109 mortar composition and graded standard sand, which will permit direct comparison of ASTM and European standard test procedures.
Role of Fly Ash and Aluminum Addition on Ettringite Formation in Lime-Remediated Mine Tailings
Authors: Mohamed AMO , Hossein M , Hassani FP
Published: January 2010

In this study, experiments were performed to evaluate the formation of ettringite in mine tailings samples treated with lime, fly ash type “C,” and aluminum. The success of the treated samples was evaluated based on results of X-ray diffraction and scanning electron microscopy. Using lime and fly ash, the preliminary investigation showed that addition of 5 % lime and 10 % fly ash constitutes the threshold of the treatment agents needed to form ettringite. However, long-term hydration resulted in lowering pH, and disintegration of formed ettringite. To overcome this problem, aluminum was added to the samples and formation of ettringite was monitored over a period of 660 days. Experimental results indicated that on availability of aluminum for reaction, primary and secondary ettringite minerals are formed and precipitated in these samples. Furthermore, the analysis indicated that the formed ettringite minerals remained stable during a hydration period of 660 days.
Proposed Universal Accelerated Test for Alkali-Aggregate Reaction The Concrete Microbar Test
Authors: Grattan-Bellew PE , Cybanski G , Fournier B , Mitchell L
Published: January 2010

The Concrete Microbar Test is modified after a Chinese test, for alkali-carbonate reactive aggregates. The protocol for the test is essentially the same as for ASTM C 1260, Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar Bar Method), except for the size of the bars, the grading of the aggregate, the water to cement ratio and the length of the test. The concrete microbars are 40 by 40 by 160 mm. The aggregate is graded to pass a 12.5 mm sieve and be retained on a 4.75 mm sieve. The water to cement ratio is 0.33. The length of the test is 30 days in 1 M sodium hydroxide (NaOH) at 80°C. The test results show that the method is applicable to both alkali-carbonate and alkali-silica reactive aggregates. Moderate correlation was found between the expansions measured in this test at 30 days, and in the concrete prism test (CSA A23.2-14A) at 1 year. Alkali-carbonate reactive aggregates may be distinguished from alkali-silica reactive aggregates in this test by replacing a portion of the portland cement by a supplementary cementing material. The expansions of alkali-silica reactive aggregates, in this test, are significantly reduced by the presence of the supplementary cementing material but expansion of alkali-carbonate reactive aggregates is largely unaffected. It is tentatively suggested that the expansion limit to separate deleteriously alkali silica reactive siliceous limestones from innocuous limestones is 0.140 % at 30 days; the proposed limit for all other aggregates is 0.04 %.
Multi-Scale Microstructural Modeling of Concrete Diffusivity: Identification of Significant Varibles
Authors: Bentz DP , Garboczi EJ , Lagergren ES
Published: January 2010

The ability to predict the expected chloride diffusivity of a concrete based on its mixture proportions and field-curing conditions would be of great benefit both in predicting service life of the concrete and in developing durability-based design codes. Here, a multi-scale microstructural computer model is applied to computing the chloride diffusivities of concretes with various mixture proportions and projected degrees of hydration. A fractional factorial experimental design has been implemented to study the effects in the model of seven major variables: water-to-cement (W/C) ratio, degree of hydration, aggregate volume fraction, coarse aggregate particle size distribution, fine aggregate particle size distribution, interfacial transition zone thickness, and air content. Based on this experimental design, W/C ratio, degree of hydration, and aggregate volume fraction have been identified as the three major variables influencing concrete diffusivity in the model. Following identification of the significant variables, a response surface design has been executed and least squares regression used to develop a simple equation for predicting chloride ion diffusivity in concrete based on these three parameters. This simple equation essentially summarizes the complicated simulations involved in computing the model response. Finally, simulations have been conducted to examine the extent of the surface layer in cast-in-place concrete, where the local aggregate volume fraction near the surface is less than that to be found in the bulk of the concrete.
Evaluation of Rubber-Filled Concrete and Correlation Between Destructive and Nondestructive Testing Results
Authors: Goulias DG , Ali A-H
Published: January 2010

Over recent years significant emphasis has been placed on the use of recycled products in highway and construction materials. Waste materials, such as tire rubber, plastic, and glass may be used with conventional materials either as aggregate replacement or binder enhancement. For portland cement concrete, rubber from granulated tires may be used as an elastic aggregate modifying the brittle failure of concrete and increasing its ability to absorb higher amounts of energy before failure. The replacement of coarse aggregate with rubber particles may significantly compromise strength characteristics of concrete due to the high compressibility of rubber particles, generating localized stresses and bonding problems between the rubber particles and the cement matrix. To the contrary, the use of fine graded rubber as partial replacement of fine aggregates may produce a ductile behavior with large deformations prior to full disintegration of concrete and affect to a lesser degree the strength loss.

An experimental study is being conducted to evaluate the effects of incorporating crumb rubber, very fine tire rubber particles, into Portland cement concrete. The objective of the study is to evaluate the effects of rubber aggregate into portlant cement concrete (PCC) properties. Initially, the rubber content replacing fine aggregates into the concrete mix was investigated by examining the concrete failure characteristics and the amount of energy absorbed during testing. The destructive testing results of the rubber-filled concrete were then coupled with nondestructive testing (NDT) evaluation. The scope of this effort was first to use a well-accepted NDT method for evaluating this specific PCC type, and second, to correlate strength and static elastic modulus to parameters evaluated from the dynamic NDT testing. These relationships may be used for estimating concrete strength and static elastic modulus from NDT results. Nondestructive testing techniques are relatively simple and quick to perform and provide the advantage of using the same samples again and again. NDT techniques are also of particular value in quality control testing.
Changes in ASTM Type II Portland Cement from 1940 to 1994
Authors: Poole TS
Published: January 2010

Historical changes in the specification requirements and properties of ASTM C 150 Type II portland cement are traced from 1940 to 1994. A general trend has been for the strength and heat of hydration properties of Type II cements to converge on the properties of Type I cements. The implications of this trend are discussed.
Influence of Penetrating Chlorides on the Pore Structure of Structural Concrete
Authors: Suryavanshi AK , Swamy RN
Published: January 2010

The present experimental investigation examines the influence of penetrating chlorides on the pore structure of structural concrete. For this purpose, the pore structure of concrete subjected to chloride penetration is compared with that of a similar concrete isolated from chlorides. To achieve the present objective, partially protected concrete slabs were exposed to chlorides for about two years by ponding with an aqueous solution of sodium chloride from the cast face. On completion of the exposure regime, the pore structure of concrete exposed to chlorides was compared with that of the adjacent concrete isolated from chloride intrusion. The concrete subjected to chloride intrusion showed a significant reduction in the number of coarser pores compared to the adjacent concrete isolated from chlorides. Various possibilities, such as degree of carbonation and degree of hydration were examined, step by step, to explain the observed modifications to the pore structure. It is shown that these results strongly suggest that the voluminous chloride-bearing compounds, such as Friedel's salt and calcium chloride, preferentially precipitate in the coarser pores, and thereby decrease the number of coarser pores. Although chloride contamination may thus result in some blocking of the pores in the cover concrete, it is unlikely to enhance the overall durability of the concrete. Further intrusion of chlorides may be hindered for a short time, but it cannot be prevented, and will continue in course of time.
Expansion of Cement Containing Crystalline Magnesia With and Without Fly Ash and Slag
Authors: Liu Z , Tang M , Cui X
Published: January 2010

Crystalline magnesia (periclase) is traditionally considered an undesirable compound in cements since it hydrates slowly at normal temperatures and, hence, causes a delayed expansion. This delayed expansion may be more harmful to the concrete structure than the “early” expansion due to free lime hydration in terms of the soundness of cements. Autoclave expansion tests, such as ASTM C 151, were designed to determine the soundness of cements containing MgO or CaO, or both. On the other hand, the controlled expansion of cements containing magnesia is beneficial, especially to mass concrete. The rate and amount of expansion of cements containing magnesia depend on many factors including the quantity, fineness and calcination temperature of magnesia, cement constituents and strength, presence of mineral admixtures such as fly ash and slag, and storage or service conditions (temperature and moisture). The expansion behavior of portland cements containing magnesia under normal (service) conditions is different from that under the autoclave conditions (high temperature and high pressure). The expansion behavior also differs in the presence of fly ash and slag. The autoclave expansion of portland cement containing magnesia is larger than the expansion at normal temperatures. In the presence of slag, however, cement containing magnesia expands less under the autoclave conditions than under the normal conditions. This implies that one should be cautious when applying the autoclave expansion test to the cement containing slag or other mineral admixtures. The addition of fly ash and slag reduces the expansion of cements containing magnesia with their increasing concentrations. Fly ash is more effective in reducing expansion of cements containing magnesia than slag at the same concentration. These results are summarized in this investigation.
Soundness Characteristics of Portland Cement-Fly Ash Mixtures
Authors: Schlorholtz SM
Published: January 2010

The Materials Analysis and Research Laboratory has been monitoring the soundness of several sources of fly ash since the early 1980's. The soundness tests were generally conducted in accordance with ASTM Test Method C 311 (the autoclave expansion test utilizing 20% fly ash and 80% portland cement, specimens prepared at normal consistency). To date, several thousand tests have been performed on various samples of fly ash that were submitted to the laboratory. Also, additional studies were conducted to investigate the influence of water content (W/CM ratio) and curing regime on the volume stability of portland cement pastes containing a fly ash that exhibited soundness problems.
A Practical Method to Solve Slump Loss Problem in PNS Superplasticized High-Performance Concrete
Authors: Jiang S , Kim B-G , Aïtcin P-C
Published: January 2010

Using the mini-slump and slump tests, three low-alkali Portland cements were found to be incompatible with a PNS superplasticizer in terms of fluidity loss in cement pastes and con-cretes having low W/C ratios (0.30 to 0.35). The addition of a small amount of sodium sulfate appeared to be a practical method to solve the slump loss problem of these superplasticized cement pastes and concretes.

The addition of sodium sulfate between 0.2 to 0.8% (or at a Na2O eq. of 0.10 to 0.35%) significantly reduces the rate of the slump loss and maintains a high slump value over 90 min after mixing of the superplasticized concrete mixes having a W/C ratio of 0.30. Moreover, the addition of sodium sulfate was not found to affect the air content of the fresh concretes. The setting of the concretes are retarded or accelerated by no more than 2 h depending on the amount of sodium sulfate added. Furthermore, the addition of sodium sulfate up to 0.5% to the superplasticized concretes increases not only the 1-day compressive strength but also the 28-day compressive strength. The addition of sodium sulfate over 0.5% was found to increase the 1-day compressive strength but to decrease the 28-day compressive strength.
Delayed Ettringite Formation at Brewer Stadium, Boone, North Carolina
Authors: Ozol MA , Strand W
Published: January 2010

Brewer Stadium, Appalachian State University, Boone, NC, was constructed in 1962 using steam-cured precast lightweight concrete channel sections for the bleacher seats. Spalling of the bleachers was observed within a few years. By 1995, approximately 375 of 860 precast elements exhibited sufficiently severe cracking and delamination that reconstruction of the stadium was the most economical alternative.

The destructive process causing the cracking and delamination of the 375 units is DEF. The (fibrous, crystalline) ettringite occurs in the concrete intergrown in the paste, in veins and cracks throughout the mortar, filling voids in the mortar, and as rims in the paste around coarse- and fine-aggregate particles. Also observed, in the same spatial relationships as the crystalline ettringite, and commonly intergrown with it, was a clear, gel-like material with low-order, mottled birefringence. This appears to be the same proto-ettringite material as described by Mielenz et al. (1995).

Visibly undistressed members exhibit incipient forms of the same DEF features that are well developed in the distressed members. Sulfate analyses show no difference between distressed and undistressed members.

The physical and chemical circumstances of the failure conform to the model presented by Heinz and Ludwig, whereby cements capable of promoting DEF meet the sulfate limitations of ASTM Specification for Portland Cement (C 150), and DEF occurs due to excessive temperature reached during heat curing of concretes made with cements of a particular sulfate to alumina ratio.

These results support the view that revisions to current standards for portland cement are unnecessary, and that what is necessary is adherence to maximum temperature guidelines during production of heat-cured concrete products.

Petrographic evidence supports the view that expansion due to DEF is caused by swelling of a proto-ettringite gel—by water absorption, similar to alkali-silica gel—that forms in the paste and that later, following expansion and crack formation, crystallizes in the cracks and peripheral separations, forming the familiar veins and rims of fibrous ettringite.

This mechanism speaks to the origin of the expansive force in the general case of sulfate attack, and to why the formation of the delicate, fibrous, ettringite crystals in the cracks is not the mechanism that exerted sufficient force to cause the cracks in which the ettringite occurs.
Autoradiographic Methods for Identifying Alkali-Silica Reaction Gel
Authors: Livingston RA , Aderhold HC , Hover KC , Hobbs SV , Cheng YT
Published: January 2010

The current method for identifying ASR gel uses ultraviolet fluorescence to image the distribution of a uranyl acetate stain that has a high affinity for the silica gel. However, UV fluorescence can also be produced by other minerals. As an alternative, methods based on imaging natural or activated radiation have been investigated. Potassium in the gel can be imaged by both the beta and gamma ray radiation of 40K. The storage photostimulable phosphor imager (SPP) system can have spatial resolution as fine as 50 μm and a dynamic range of >105. Digital images of 40 K distribution in actual concrete cores with K2O% <1% have been acquired with counting times on the order of 24 h. Similarly, using the conventional uranyl acetate stain approach, the distribution of uranium can be imaged by the natural radioactivity of its daughter products, using the SPP plates with counting times on the order of 7 days. Alternatively, the uranium can be imaged by inducing fission and using fission track detectors. Autoradiography can thus be used to survey concrete structures for areas of possible ASR. Further research is necessary to standardize the methods and to evaluate their performance relative to the conventional stain methods.
Determining Elastic Properties of Concrete Using Vibrational Resonance Frequencies of Standard Test Cylinders
Authors: Kolluru SV , Popovics JS , Shah SP
Published: January 2010

A technique for determining the elastic material constants of a concrete test cylinder from longitudinal resonance frequencies is proposed in this paper. The proposed technique permits calculation of both the material constants (E and μ) from one relatively simple measurement. The formulation is based on an accurate three-dimensional vibration analysis of intermediate length cylinders using the Rayleigh-Ritz method. First, the test procedure is described and an illustrative example is given. The accuracy of the method is then verified through tests on steel and aluminum cylinders. Test results from concrete cylinders are then presented. A favorable comparison between the values of the elastic modulus predicted by the proposed technique, the standard ASTM test procedure and direct mechanical measurement is shown.
Alkali-Silica Reaction in Concrete Caused by Densified Silica Fume Lumps: A Case Study
Authors: Marusin SL , Shotwell LB
Published: January 2010

Petrographic and scanning electron microscopy (SEM) studies of a lightweight aggregate concrete exhibiting severe cracking indicate that a relatively large, nonuniformly distributed and densified formation (lumps) of silica fume (SF) may have substantially contributed to the mechanism of concrete deterioration. The lumps of SF (from 100 to 800 μm in size) were observed to react in a manner similar to reactive aggregates with cement alkalies to form silica gel. Such an alkali-silica reaction (ASR) is often associated with an expansion that leads to cracking of concrete. The poor dispersion of SF also increases the effective water to cement-plus- pozzolan ratio of portions of the concrete, possibly contributing to drying shrinkage cracks. The early drying shrinkage cracks may have led to increased water penetration and subsequent ASR.
Properties of Concrete with Ground Ultrafine Phosphorus Slag
Authors: Feng NQ , Shi YX , Ding JT
Published: January 2010

Ultrafine phosphorus slag (UFPS) with surface area greater than 6000 cm2/g is a vitreous powder similar to granulated blast-furnace slag (GBFS). The comparative investigation of UFPS and GBFS in this paper showed that UFPS could improve the fluidity, strength, and durability of concrete at partial replacement of cement. With 275 kg/m3 compound UFPS, 27 5 kg/m3 Grade 525# ordinary portland cement, 0.26 water-binder ratio, and 9.7 kg/m3 high-range water-reducing admixture (HRWRA), a concrete had been prepared with a slump of 240 mm, 28-day compressive strength 101 MPa, and a diffusion coefficient of Cl about one third lower than that of the control portland cement concrete.
A Kinetic-Based Method for Interpreting ASTM C 1260
Authors: Johnston D , Stokes D , Surdahl R
Published: January 2010

A proposed kinetic-based method for interpreting ASTM C 1260 test results is introduced that appears capable of overcoming some of the shortcomings currently encountered using a percent expansion criterion for defining potentially reactive aggregate. The method is based on nucleation and growth or phase transformation reaction kinetics where the percent expansion is exponentially related to a power of time. Solving the logarithmic form of the kinetic equation by a least-squares fit yields two parameters, lnk and M, where lnk is the intercept and M is the slope of the regression line, which can be used to determine potential reactivity. A plot of M versus lnk yields two separate domains—one containing reactive aggregate and one containing innocuous aggregate. Values of lnk < -6 are associated with innocuous aggregate. The method successfully differentiated between several reactive aggregates with 14-day expansions of less than 0.1% as reactive and indicated that one aggregate with a 14-day expansion of 0.278% was innocuous. The method also appears promising with regard to determining effective levels of pozzolans and other admixtures for mitigation of ASR reactive aggregate.
Evaluation of the Potential of Densified Silica Fume to Cause Alkali-Silica Reaction in Cementitious Matrices Using a Modified ASTM C 1260 Test Procedure
Authors: Rangaraju PR , Olek J
Published: January 2010

Numerous research and field studies in the past have shown the ability of silica fume to improve the mechanical and durability properties of concrete. Despite these beneficial effects, some recent studies have raised concerns about the dispersibility of a few commercial dry densified silica fumes and the potential for development of alkali-silica reaction associated with the presence of undispersed agglomerates of silica fume in cement matrices.

In light of these developments, the present investigation focuses on determining the potential of undispersed silica fume agglomerates to participate in the alkali-silica reaction and the influence of such factors as size and morphology of the agglomerates on the extent of this reaction. An experimental program consisting of a modified ASTM C 1260 test procedure was used to identify and study distress associated with the presence of undispersed silica fume in cementitious pastes and mortars.

Results of this investigation indicate that undispersed silica fume agglomerates in cementitious pastes actively participate in alkali-silica reaction. The nature and the magnitude of the observed distress were found to be distinctly dependent on factors such as the size of the agglomerates, their morphology, and the water-binder ratio of the cementitious matrix. In addition, this paper presents suggested modifications to the ASTM C 1260 procedure to test for the reactivity of silica fume agglomerates.
Proportioning Concrete Mixes with Quarry Wastes
Authors: Nataraja MC , Nagaraj TS , Reddy A
Published: January 2010

An integral part of concrete mix proportioning is the preparation of trial mixes and making adjustments to such trials striking a balance between the requirements of placement, strength, and durability. When coarse aggregate characteristic strength is lower than the levels of strength of the concrete desired, different methods, viz., British, ACI, and the country's standard code, cannot be used directly. In this paper a generalized method is advanced to proportion concrete using quarry wastes, namely, cuddapah and marble in concrete, as coarse aggregate. Concrete is regarded as a composite of cement mortar matrix and coarse aggregate. The basic principle of the method is to assess the characteristic strength of coarse aggregate from compressive strength data of concrete failed by aggregate fracture and from that characteristic strength to assess the cement mortar strength required so as to ensure the development of the required strength of concrete. To arrive at the exact water-cement ratio of mortar matrix, the generalized Abrams' law is used.
Analysis of the Granular Structures of Aggregates Using Solid Volume Measurement of Elementary Fractions
Authors: Lecomte A , Mechling JM
Published: January 2010

This article deals with the measurement of the solid volumes and hence the packing density of elementary fractions of aggregates, a parameter used in modern methods for the optimization of granular mixtures. After reviewing methods for measuring solid volumes, two examples are presented to illustrate the relevance of the proposed method in elucidating the internal structures of aggregates, their morphological properties, and the state of the surfaces of their grains. The solid volumes data not only enhance standard characterization of aggregates but also underline the need to closely relate aggregate identification data with the geological history of the site where aggregates are extracted.