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Confirms that the strengths of capped concrete test cylinders cast in waxed paper molds are less than those made in metal molds with identical procedures. Shows that the major difference in strength is attributed to the higher density of the cylinders cast in metal molds. Suggests that a heavier reusable base plate might be used with waxed paper molds. [ABSTRACT FROM AUTHOR]

A number of bonded overlays using portland cement grout have been employed in resurfacing pavements since 1954. This paper presents results of a survey on a number of these pavements to ascertain the performance of the overlays. The overlays were sounded and their surfaces inspected visually. Cores were taken to confirm areas of bond distress. Some of the specific projects surveyed are described. The introduction to the paper outlines some of the more important pub-lished material on the proper methods and techniques of bonding new con-crete surfaces to old concrete surfaces. [ABSTRACT FROM AUTHOR]

The paper relates to a research project carried out in the Department of Building, UMIST in conjunction with the Building Research Station into the development of techniques for the measurement of dimensional inaccuracies of strong height pre-cast concrete units up to 8 m long.
This resulted in the design of new and inexpensive instrumentation based on that already commercially available, which was applied to determine the degree of deviation to be expected in the production of these units. Particular emphasis is given to the measurement of form deviation, or twist, and the problems concerned with its determination in the factory environment. The inherent dimensional inconsistencies resulting from the material used and manufacturing processes is briefly reviewed.
The paper examines the validity of recognized metrological concepts in the context of the increasing emphasis upon prefabricated component assemblies as an integral part of the building process, and discusses the relationship between the requirements of accuracy control dictated by the assembly procedures on site and those likely to be achieved by the production processes in the factory. The problems of setting standards for tolerances in realistic terms are considered in the light of current practice in the detailing of this form of construction and are related to the production inaccuracies involved. [ABSTRACT FROM AUTHOR]

Existing methods of selecting proportions for concrete usually offer tabulated values as guides in approaching the optimum amount of water, cement, and aggregates. For more accurate estimates, tables are presented in this paper which were developed recently for the State Highway Department of Alabama. One of these fables refers to the adjustments in water content for slump. In other tables, cement factors, in bags per cubic yard, are presented as a function of mix prqportion, grading, and average specific gravity of mineral aggregate. Further tables are offered to obtain the average specific gravity of mineral aggregate when a mixture of two materials of different specific gravities are used. Numerical examples illustrate the use of the tables pre-sented. While these tables are not a self-sufficient method of concrete mix proportioning, they will reduce the number of trial mixtures required. [ABSTRACT FROM AUTHOR]

This paper, written in conjunction with the work of ACI Committee 348, Structural Safety, presents some thoughts and guidelines on avoidance of gross errors, the major cause of failure of structures. It is recognized that these thoughts are not new and that many of them are equally applicable to the design and detailing of structures in materials other than reinforced or prestressed concrete. Fur-thermore, they are not complete, for only the de-sign engineer, working on his specific project, can anticipate every possible danger flag. [ABSTRACT FROM AUTHOR]

Copyright of Rock Mechanics (00357448) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Considers the factors which affect the optimum coarse aggregate content in proportioning a concrete mix. Weymouth's theory of particle inter-ference, as extended by Butcher and Hopkins, is examined and further modified. [ABSTRACT FROM AUTHOR]

A continuing inspection by nonoperating personnel was organized some 20 years ago to assess the condition of structures making up a large hydroelectric power system. The purpose of this program is to ensure that all structures are maintained in such condition that they can safely perform all functions for which they were designed. A secondary result of the inspection is the virtual elimination of major unforeseen maintenance expenditures. As a part of this service, the cause of the deterioration of structural materials is determined, if possible, before recommendations for repair complete with cost estimates are submitted to the owner. The program has been developed to such a stage that major items of concrete maintenance can be scheduled 5 years in advance, with a tentative schedule drawn up for the following 5 years. This paper is limited to methods of concrete inspection and maintenance. Methods of concrete repair found to be suitable in the area, which extends to the southerly limit of the boreal or northern climatic region, are described briefly. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the American Concrete Institute is the property of American Concrete Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Presents results of an experimental study of the effect of temperature changes between room temperature and 212 F on deflections of cement paste and mortar beams under load. It was found that: (a) cement paste and mortar beams deflect exces-sively when heated after application of load; (b) deflections occasionally lead to failure at low stresses and after moderate heating; (c) deflections increase with increasing rate of heating; (d) deflections are larger and the temperature at failure is lower for cement paste than for cement mortar; (e) deflections are larger and the temperature at failure is lower for saturated than for dry beams; (f) rapid rates of heating permanently reduces the modulus of elasticity of cement mortar, indicating internal destruction of the material structure; (g) thermal cycling leads to excessive deflections and occasionally to failure. A tentative explanation of the phenomena observed is suggested. [ABSTRACT FROM AUTHOR]

The stress-strain relationship in compression of hydrated portland cement (with a water-cement ratio of 0.33) and a lightweight concrete was studied at elevated temperatures. The properties of both materials seemed to be virtually unaffected by temperature up to about 400 F. Above this, the modulus of elasticity and ultimate strength decreased with increasing temperature. These changes were more definite for hydrated portland cement. [ABSTRACT FROM AUTHOR]

The authors classify as "strengthened" that concrete which has less than specified minimum reinforcement thus distinguishing it from "plain" concrete and "reinforced" concrete. An approach to design is described for ground supported elements which introduces a straight-line transition between the stress, as a function of moment capacity, developed by the plain concrete and that produced by the minimum reinforcement using working stress design. With this approach, amounts of reinforcing steel below the specified minimums are given credit for serving as a "strengthening" influence on plain concrete [ABSTRACT FROM AUTHOR]

Recommendations for producing good interior and exterior portland cement plastering are described. Subjects covered are: important factors involved, materials, proportioning and mixing, sampling and testing, methods of application, bases, crack control, application and curing, and decorative finishes. [ABSTRACT FROM AUTHOR]

While there is a great deal of variety in the United States in the design of concrete highway pavements, there have been trends toward uniformity that can be noted. Among the items where a trend toward uniformity has been noticed are: subbase requirements, pavement cross sections, pavement types, slab lengths, and joining practices. [ABSTRACT FROM AUTHOR]

Quality of a concrete slab or floor is highly dependent on achieving a hard and durable surface which is plane and free of cracks. The properties that the surface has are determined by the quality of the concreting operations. Furthermore, timing of these concreting operations and finishing techniques is critical. Otherwise, undesirable changes occur at the wearing surface; these may lead to soft or dusting surfaces, permeable concrete, cracking, and poor durability. This recommended practice tells how to produce good quality floors and slabs for various classes of service, emphasizing such aspects of construction as site preparation, concreting materials, concrete mixture proportions, concreting, workmanship, and curing. Adequate supervision and inspection are required of all job operations including particularly those of finishing. [ABSTRACT FROM AUTHOR]

Quality of a concrete slab or floor is highly dependent on achieving a hard and durable surface which is plane and free of cracks. The properties that the surface has are determined by the quality of the concreting operations. Furthermore, timing of these concreting operations and finishing techniques is critical. Otherwise, undesirable changes occur at the wearing surface; these may lead to soft or dusting surfaces, permeable concrete, cracking, and poor durability. This recommended practice tells how to produce good quality floors and slabs for various classes of service, emphasizing such aspects of construction as site preparation, concreting materials, concrete mixture proportions, concreting, workmanship, and curing. Adequate supervision and inspection are required of all job operations including particularly those of finishing. [ABSTRACT FROM AUTHOR]

The resistance of concrete to chemical attack may often be enhanced or maximized by careful attention to concrete proportioning, mixing, placing, and curing procedures. However, in a number of situations concrete must be protected by barrier materials which prevent contact with the chemical agent. Materials available for protection have been classified here, and tables have been provided as a guide for protection against specific agents. Methods of application, with consideration for both effectiveness and safety, are discussed. The report is intended to serve as a guide prior to consultation with experts regarding the specific situation. [ABSTRACT FROM AUTHOR]

It is shown that the strengths of concrete test specimens (cylinders, cubes, and prisms) can be related to one another by simple expressions. Substantiating test results are presented. The secondary influence of the fine-ness modulus of aggregate on this relation is discussed. [ABSTRACT FROM AUTHOR]

Previous fatigue studies of concrete were in many cases not representative of the load conditions of actual structures since in these tests the applied loads fluctuated between constant minimum and maximum values. In the present investigation plain concrete specimens were subjected to repeated flexural stresses according to various load histories; the maximum load within a test was varied between two limits, or rest periods were introduced. The results were interpreted according to various physical models and compared to the Miner rule. This hypothesis may give conservative or unsafe predictions of the fatigue strength depending on the load program. An Improved design method Is suggested. [ABSTRACT FROM AUTHOR]

Describes a method for determining the thickness of a concrete slab by measuring the amount of gamma radiation that passes through it. Results in the laboratory showed that slabs could be measured to an accuracy of better than 2 percent. [ABSTRACT FROM AUTHOR]

Describes and illustrates the construction phase of the tunnels on a hydroelectric project in Shasta County, California. Traces the concrete op-eration through mix proportioning, mixing, transportation, and placing. Illustrations of specialized transporting and handling equipment are presented. [ABSTRACT FROM AUTHOR]

A study of the compacting-factor method of measuring workability of small-aggregate concrete (1½ in.) indicated that: (a) the degree to which concrete heaps when a mold is allowed to overfill from the discharge of a mixer reaches a maximum at an intermediate workability and decreases as the mixture gets either drier or wetter; and (b) the net, loose weight of concrete in a mold after strike off increases with increasing workability. The net, loose weight of concrete in a mold filled to overflowing and then struck off could form the basis for controlling workability of mixtures having a slump not greater than 3 in. Studies using mixtures with 6-in. aggregate indicated that heaping weight, struck-off weight, and compacting factor increase with increased water content until the slump reaches from 1½ to 3 in. and then they decrease. Routine determinations of heaping weight or struck-off loose weight might be used to detect batches of excessive or deficient water content which could be rejected before delivery to the forms. [ABSTRACT FROM AUTHOR]

Results of detailed research and investigation of field problems have demonstrated that chlorides in concrete can cause severe corrosion of alu-minum when coupled to steel. The expansive nature of the corrosion products causes cracking and spalling of concrete cover over embedded aluminum conduit. Chloride anion enrichment, as a result of the galvanic connection, serves to arrest polarization of the aluminum. Production of an aluminum chlorhydroxide product and a specially oriented "cubic" attack pattern have been typical of this reaction in both field and laboratory experiences. A similar ion migration mechanism might be expected for any metal whose composition or state of stress make it anodic to other coupled embedded metals. In chloride-free concrete, aluminum has good resistance to corrosion both alone and coupled to steel and no cracking of concrete has been encountered. It is recommended that chloride additions or contaminations should be avoided in concrete containing embedded metals. If this is not practicable, protective coatings are required and are available. [ABSTRACT FROM AUTHOR]

Data on creep of concrete, both mass- and water-cured in the temperature range 70 to 205 F are presented, together with results of subsequent creep recovery tests. Hence, observations on the viscous character of the creep deformation are made. Data on strength and elasticity of one mix within the same temperature range are presented. [ABSTRACT FROM AUTHOR]

Stresses in concrete are modified by the effects of creep and shrinkage, and can be estimated only if these data are known. A solid model which approximates the structure of concrete is proposed and is used to predict creep and shrinkage strains for concretes containing various aggregates of many mix proportions, from data relating to the constituent materials. Model predictions are compared against experimental results and it is concluded that an advantage of the model has been its ability to predict time-dependent strains in concrete from a minimum of experimental data. [ABSTRACT FROM AUTHOR]

Analytical and numerical methods are presented for the computation of creep of concrete when the stress-strength ratio varies with time. The computations are based on a "standard" creep curve for a concrete of constant strength. [ABSTRACT FROM AUTHOR]

The general requirements for producing satisfactory concrete during cold weather are discussed, as are methods for achieving these requirements. It Is emphasized that for many structural concretes, protection considerably in excess of that required to insure freedom from damage by early freezing is required to assure safe development of strength. Accelerators, keeping of temperature records, heating of materials, subgrade preparation, protective insulating coverings, heated enclosures, curing, and form removal are discussed. Supplementary material on the effect of curing temperatures on concrete strength is referenced in authoritative sources. A list of selected references is included. [ABSTRACT FROM AUTHOR]

Rapid drying on the exposed surface of concrete may result in finishing problems such as stickiness, sponginess, and unevenness; plastic shrinkage and cracking; or a compacted surface which creates a layered structure subject to scaling. These undesirable characteristics may be corrected by control of evaporation with a monomolecular film on the surface of bleeding water. Laboratory tests and field experiences are discussed. [ABSTRACT FROM AUTHOR]

Any sound concrete, in sections of sufficient thickness, can be used to construct a satisfactory biological shield. When space permits, conventional concrete is the most economical, satisfactory shield against radiation. However, when space is a consideration, high density concrete can be used for shielding. Most high density concrete for shielding has been made with naturally occurring iron ores, titaniferous iron ores, "hydrous iron ores, and barite. Although structural strength is an important factor in high density concrete, workability and density have been the major factors previously studied. This investigation showed that high strength concrete can be made using materials that provide high density, and that high density concrete can be made using proportions that ensure high strength. When high strength and high density are both desired, they can be attained by a direct combination of the standard practices developed for attaining each condition separately. Concrete made as part of this study using magnetite aggregate or ilmenite aggregate having a hardened unit weight of about 230 lb per cu ft had a compressive strength of 9000 psi at 7 days and I 1,000 psi at 28 days. [ABSTRACT FROM AUTHOR]

A theory of the influence of aggregate properties on concrete shrinkage is presented. An equation is derived from which the shrinkage of concrete may be computed from the fractional volume, the modulus of elasticity, and the shrinkage of cement paste and aggregate. A comparison is made between theoretical and experimental results. [ABSTRACT FROM AUTHOR]

Expansive cements and concretes, although seemingly new engineering materials, have had a long history of development. During the past 74 years, there have been recurrent efforts to develop expansive cements. However, only in the last 15 years has there been successful production and application of such cements to controlled expansive concretes. Historical developments of expansive cements in France, the Soviet Union, and the United States are briefly reviewed; salient properties of self-stressing, and shrinkage-compensated, expansive cements and concretes are summarized; current applications of expansive concretes are examined; and their potential uses are indicated. [ABSTRACT FROM AUTHOR]

The formation of a deposit of ettringite in a submerged dam gallery is described. It occurred in an area where a fly ash-cement mixture had been used for the placement of prepacked concrete. Where fly ash was used to replace a portion of the cement in conventionally placed concrete nearby, no such deposit was observed. No evidence of deterioration of the concrete could be found. The deposit was found adjacent to a 'stop-work' plane in the grouting of the aggregates, and it is thouqht that the concrete at this point could have become enriched in lighter hydration products (e.g., calcium sulfoaluminate, calcium hydroxide J and grout admixtures. The formation of ettringite as a stable product of cement hydration would have been assisted by additional sulfate derived from the fly ash. It is believed that water seeping along permeable planes in the concrete dissolved some of the sulfate and alumina-containing phases formed during cement hydration and, on reaching the gallery, ettringite was precipitated from solution. [ABSTRACT FROM AUTHOR]

Experimental investigations to examine the effect of concrete sedimentation characteristics on pull-out bond strengths are reported. Concretes of the same compressive strength but varying settlement and bleeding were used with plain round, square, twisted, and deformed bars. The general trend of the results indicated that increased concrete settlement in all cases led to reduced bond of rigidly positioned, horizontal bars, even with small depths of plastic concrete beneath the bars. [ABSTRACT FROM AUTHOR]

As part of its mission, ACI Committee 116, Nomenclature, presents the fifth published installment of a glossary of terms on cement and concrete technology. The glossary has been divided into 13 increments which are being presented to elicit discussion as they are completed, regardless of order. Following publication and discussion of the final installment, the committee will review and combine the groups for consideration as an ACI standard. [ABSTRACT FROM AUTHOR]

The strength contribution of a pozzolan of volcanic origin in pozzolan-cement concretes with 15 to 35 percent replacements, as a function of the replacement of portland cement by pozzolan, with cements of different qualities was studied. The term "strength contribution" of a pozzolan, in pozzolan-cement concretes is defined. [ABSTRACT FROM AUTHOR]

On the basis of general theories for two-phase materials, formulas have been derived from which the modulus of elasticity can be calculated for concrete, cement mortar, and cement paste, when the modulus is known for the component materials. Experimental verification is offered and a numerical example is worked out which illustrates practical application of the formulas. [ABSTRACT FROM AUTHOR]

Traces the development of slip-form concrete paving in the United States. Covers the period since the first half-mile project was built in Iowa in 1949 through the 1963 construction season when several hundred miles of paving were built with slip-form pavers. The early developmental machines are described and the newer improved and electronically controlled slip-form pavers which are now being used to build high-speed turnpikes, expressways, and interstate highways as well as light traffic secondary roads are also discussed. The principles of slip-form paving are described, the requirements for ade-quate subbase preparation are discussed and some of the important con-siderations for proper mix proportioning are outlined. Illustrations of slip- form pavers for a wide variety of projects, which demonstrate the versatility of this equipment, are presented. Offers some of the data to date which prove the excellent riding qualities which can be obtained through the use of slip-form construction. [ABSTRACT FROM AUTHOR]

Development of criteria for the prediction of thermal stresses in concrete dam construction block during cooling operations prior to grouting is outlined. A new concept is presented concerning the tensile stress within a block which inc I udes the ratio of the height of the temperature transition zone to the base length of the block being cooled. It is shown that high temperature gradients in a concrete block will lead to excessive tensile stresses resulting in cracking of the block. Control of the maximum stress may be achieved through cooling operations leading to acceptable temperature gradients. Several curves are given for prediction of maximum tensile stress as a function of base length, height of temperature transition zone, temperature change, and properties of the concrete. [ABSTRACT FROM AUTHOR]

This proposed standard is intended as a supplement to ACI Standard "Recommended Practice for Selecting Proportions for Concrete (ACI 613- 54)." The standard describes a procedure for proportioning concretes having slumps in the range of zero to I in. and consistencies below this range, for aggregates up to 11f2 in. maximum size. Suitable equipment for measuring such consistencies is described. Tables similar to those in ACI 613-54 are provided which, along with laboratory tests on physical properties of fine and coarse aggregate, yield information for obtaining concrete proportions for a trial mixture. Examples of the use of these tables, in conjunction with tables in ACI 613-54, are given. [ABSTRACT FROM AUTHOR]

Reports the effects of various factors on tensile and shear bond of masonry mortars with a view to establishing a basis for recommendations for obtaining strong joints. Tests were conducted to determine the effect of mortar materials, specimen storage, mortar mixes, variations in block composition, differences in block curing, and type of masonry assemblage. Also in one test series the tensile bond of epoxy adhesives used in place of mortar was investigated. [ABSTRACT FROM AUTHOR]

Elastic and inelastic behavior of mortar filled tubes in compression was investigated. The work was restricted to seamless steel tubes ranging from 1 to 3 in diameter. Experimental values of the ultimate axial load capacities are compared to the theoretical values obtained from the tangent modulus formula. [ABSTRACT FROM AUTHOR]

Reports results of an Investigation of the effect of replacing the fines of four particular structural lightweight aggregates with equal volumes of natural sand. Cement contents were varied to obtain compressive strengths over the range of 3000 to 6000 psi. A comparison of the reported physical properties for lightweight concrete was provided by tests of normal weight concrete of corresponding compressive strength. The test results are presented for each of the lightweight aggregates showing the mix and physical properties, as functions of the partial or complete fine aggregate replacement, for concretes at compressive strength levels of 3000, 4000, 5000, and 6000 psi. in general, the structural properties were improved as the amount of natural sand was increased, but this improvement was achieved only with considerable increase in the unit weight. Decrease of total water and cement contents required for a given slump and compressive strength were greater for the harsher crushed aggregates. [ABSTRACT FROM AUTHOR]

As part of its mission, ACI Committee I 16, Nomenclature, presents the third published installment of a glossary of terms on cement and concrete technology. The glossary has been divided into 13 increments which are being presented to elicit discussion as they are completed, regardless of order. Following publication and discussion of the final installment, the committee will review and combine the groups for consideration as an ACI standard. [ABSTRACT FROM AUTHOR]

The standard procedure for making concrete test cylinders tends to bring water to the top of the cylinder. Presents experimental results to show that standard 6 x 12 in. concrete cylinders are not of uniform strength and that the top one-third is the weakest part. [ABSTRACT FROM AUTHOR]

Tests were made on 6-in. cubes from 17 different batches of concrete. Some of the cubes were cured in water and tested in a standard compression machine. The remaining cubes were steam cured and tested with the rebound hammer prior to being loaded to failure in a compression testing machine. The results suggest that the rebound hammer may be used in conjunction with some method of accelerated curing to provide a rapid and convenient field method for estimating the strength and quality of concrete. [ABSTRACT FROM AUTHOR]