Search

The freezing and thawing resistance of 47 structural lightweight concretes containing seven light-weight aggregates and varying amounts of natural sand fines are reported. This paper is fourth in a series regarding the partial or complete replacement of lightweight fines with sand. The seven lightweight aggregate concretes and companion sand and gravel aggregate concrete were evaluated at nominal compressive strengths of 3000 and 5000 psi. The level of durability was generally raised when increasing amounts of sand fines were used in the 3000-psi concretes. All 5000-psi concretes were highly durable and the use of sand fines provided only minor improvements in this case. [ABSTRACT FROM AUTHOR]

The creep and shrinkage volume changes of 47 structural lightweight concretes containing seven lightweight aggregates and varying amounts of a natural sand are reported. This paper is fifth and final in a series regarding the partial or complete replacement of lightweight fines with sand. Creep and shrinkage were generally reduced when increasing amounts of sand fines were used. Data are presented which correlate the reduced volume changes to increasing volume of coarse aggregate in the concrete. The increase of coarse aggregate volume arises from the proportioning procedures, and also reflects the reduction of water, cement, and fine aggregates in lightweight concretes containing increasing amounts of natural sand. [ABSTRACT FROM AUTHOR]

An investigation was made of the effects of steel fiber parameters and concrete mix parameters on the flexural strength properties of steel fibrous concretes and mortars. Compositions were evaluated in which the steel fiber content was as high as 4.0 volume percent. Data are presented which show the relationship of fiber content and fiber spacing on the ultimate and first crack flexural strength of a standard mortar formulation. The effect of mix workability as controlled by the mix composition on the flexural strength properties is discussed. The effect of coarse aggregate additions on the flexural strength of a steel fibrous mortar is also discussed. The use of steel wire fibers provides significant improvements in the flexural strength properties of concretes and mortars when the proper conditions of mix formulation, batching, and placing are achieved. [ABSTRACT FROM AUTHOR]

Two cases where coarse aggregate was elimin-ated from concrete and sand-cement mortar was used for construction are described. Construction sites were located in desert areas (North Africa and Arabian Gulf) where due to special conditions elimination of coarse aggregate helped expedite construction while resulting in economy. Two new methods of measuring the consistency of sand-cement mortar are explained. These meth-ods have the advantage that they can be per-formed using small quantities of sand, i.e., 50-500 g (0.1-1.0 lb) as compared to the 10 kg (22 lb) that are required for the conventional slump test. [ABSTRACT FROM AUTHOR]

Concrete sand grading is statistically analyzed. The width of each sieve opening of the different sieves is considered as the cell boundaries and the percentages by weight of sand retained on successive sieves, as the frequencies. The sand frequencies are normal log distributed. The fineness modulus Is a logarithmic function of the geometric mean of the particle size. The dispersion index is a logarithmic function of the geometric dispersion. An analysis of variance of the fineness modulus and tne dispersion index has been made to establish a sampling experiment. [ABSTRACT FROM AUTHOR]

The compressive strength of laboratory cured and field cured cylinders are compared with 4 and 6 in. diameter cores at ages up to 84 days. Nearly 500 samples of natural and lightweight concrete under simulated job conditions showed that all cores at comparable ages tested lower than cylinders. [ABSTRACT FROM AUTHOR]

A comparison is made of the various models which have been proposed to predict the depend-ence of concrete shrinkage upon the properties of its constituents and the aggregate volume concentration. The predictions of one of these models, the Cement and Concrete Association model, are compared in a general way with the observed shrinkage behavior of concrete. It is shown that the shrinkage of normal aggregate concretes is dependent primarily on only three parameters--the paste shrinkage, the aggregate shrinkage and the aggregate volume concentration. The observed dependence of concrete shrinkage upon original water content by weight, Young's modulus of the concrete and aggregate grading, for specimens of the same water-cement ratio, is shown to follow directly from the simple dependence of concrete shrinkage upon aggregate volume concentration. [ABSTRACT FROM AUTHOR]

This report presents recommendations for the production of cast-in-place architectural concrete. The importance of specified materials, forming, concrete placement, curing, additional treatment, inspection and their effect on the finished product is discussed. The report deals primarily with requirements for architectural concrete over and above normal requirements outlined in existing ACI standards. [ABSTRACT FROM AUTHOR]

The influence of maximum aggregate size on the compressive strength of concrete and microconcrete (sieved mortar), exposed to evaporation immediately after casting, was studied. The main variants were: (a) maximum aggregate size ¾ in. [19.05 mm), ½ in. (12.5. mm), ⅜ in. (9.6 mm), 3/16 in. (4.8 mm); (b) time of exposure to evaporation -- 0, 45, 90 and 300 min. Concrete and air temperature in the first 24 hr 30 C (86 F); initial rate of evaporation about 1 kg/m2/hr (0.2 Ib/sq ft/hr). It was found that the aggregate restrains the plastic shrinkage associated with drying. The resulting tensile stresses impair the properties of the concrete, as internal cracking and reduction in strength were observed. The larger the maximum aggregate size or aggregate content, the higher the internal cracking and the loss of strength after 5 hr exposure to evaporation: 21,12 and 5 percent, for concretes with maximum aggregate size of ¾, ½ and ⅜ in., respectively. [ABSTRACT FROM AUTHOR]

This recommended practice covers the construction of concrete pavements and concrete bases without attempting to include inflexible specifications for procedures, materials, or equipment. References are made to specifications, but only as a guide to enable a selection of requirements suitable for a particular location or class of work. The document is slanted to some degree toward use by agencies other than state highway departments or turnpike authorities with presumably large and experienced engineering staffs, and with knowledge of past performance of pavements in the area. Siections are devoted to specifying, sampling, and testing materials, and to the possible influence of materials on skid resistance, economy, and durability. Maximum aggregate size is mentioned as sometimes relating to pavement durability. Subgrades and subbases are treated only as to final preparation for paving. Recommendations for forms are included as well as recommendations for projects using slipforms. Arrangement of joints is described, and references are given for guidance in using reinforcement. Sections on normal and high-early-strength concrete proportioning rely heavily on reference to the report of ACI Committee 211, but point out the special problems connected with pavement concretes and the use of admixtures in pavement concrete. Sections on mixing, placing, finishing, and curing concrete refer to other ACI reports where pertinent, but make recommendations for the special handling necessary in the case of pavements. Concrete bases are treated where procedures vary from those used for pavements, and recommendations and references are given for cold and hot weather concreting. [ABSTRACT FROM AUTHOR]

Walls made from 44 different types of concrete masonry units were subjected to fire endurance tests. Tnree semiempirical formulas were used to express the fire endurance of these walls as a function of three geometric variables and two thermal properties which characterize the shape and material of the constituent masonry units. A numerical example is included to show the application of the formulas. [ABSTRACT FROM AUTHOR]

This report presents recommendations for structural design, materials, and con-struction of concrete tanks, reservoirs, and other structures commonly used in water and waste treatment works where dense, impermeable concrete with high resistance to chemical attack is required. Special emphasis is placed on a structural design which minimizes the possibility of cracking and accommodates vibrating equipment and other special loads. Proportioning of concrete, placement, curing and protection against chemicals are also described. Design and spacing of expansion and con-traction Joints receive special attention. [ABSTRACT FROM AUTHOR]

Concrete mixed, transported, and placed under conditions of high temperature, low humidity, or wind, requires an understanding of the effects such environmental factors have on concrete properties and construction operations. When these factors are understood, measures can be taken to eliminate or minimize undesirable effects. This recommended practice defines hot weather, lists possible unfavorable effects and recommends practices intended to minimize them. Among these recommendations are such important measures as precooling ingredients, limitations of concrete temperature as placed, length of haul, facilities for handling concrete at the site, and special placing and curing techniques. A selected bibliography is appended. [ABSTRACT FROM AUTHOR]

These specifications are a reference standard which the engineer or architect may make applicable to any building project by citing them in the project specifi-cations. He supplements them as needed by designating or specifying individual project requirements The document covers materials and proportioning of concrete; reinforcing and prestressing steels; production, placing, and curing of concrete; and formwork design and construction. Methods of treatment of joints and embedded items, repair of surface defects, and finishing of formed surfaces are specified. Separate chapters are devoted to slab construction and finishing, architectural concrete, massive concrete, and materials and methods for constructing post-tensioned concrete. Provisions governing testing, evaluation, and acceptance of concrete as well as for acceptance of the structure are included [ABSTRACT FROM AUTHOR]

Describes piston, pneumatic, and squeeze-pressure type pumps for transporting and placing structural concrete. Rigid and flexible pipelines are discussed, couplings and other accessories described, and delivery capacity for various sizes of lines reported. Recommendations for proportioning pumpable concrete suggest optimum gradation of aggregates; outline water, cement, and admixture requirements; and emphasize the need for field testing of trial mixes for pumpability. Importance of presoaking of lightweight aggregates is stressed. Suggestions are given for layout of lines; for maintaining uniform delivery rate as well as uniform quality of concrete at the end of the line; and for cleaning out pipelines. This report does not cover shotcreting or pumping of nonstructural insulating or cellular types of concrete. [ABSTRACT FROM AUTHOR]

A one-cycle freezing test was used fo demonstrate the effect of maximum size of aggregate on the frost resistance of concrete at a variety of water-cement ratios and degrees of saturation. After being cured for a period of at least I month the 3 x 6 in concrete specimens were conditioned to various degrees of saturation, to simulate different exposure conditions. Frost susceptibility of the various specimens was determined from the length change patterns produced in the freezing test. Maximum size of aggregate was shown to have a great effect on frost resistance. For example, the in maximum aggregate size speci-mens showed expansions during freezing, only when the water-cement ratio was as high as 0.60, while % in maximum aggregate specimens showed expansions at a water-cement ratio as low as 0.45. [ABSTRACT FROM AUTHOR]

Effects of various factors on the formation of voids in the surfaces of concrete structures com-pacted with internal vibrators were studied. Vibra-tion procedure, consistency, layer thickness, form material, release agent, and mix proportions were varied. TTie vibration procedure was the factor which had the largest influence on the surface appearance. [ABSTRACT FROM AUTHOR]

Grouts containing granulated blast furnace slag of melilitic type present a particular behavior with respect to a succession of freezing and thawing cycles. Such grouts become surrounded with a thin film of particularly resistant finely crystallized calcite which results from the presence of granulated slag in the grout. This film layer increases notably the values of tensile and compressive strengths at rupture of these grouts [ABSTRACT FROM AUTHOR]

This report presents discussion and recommendation for the fabrication, handling, and erection of precast concrete wall panels. The report covers plant facilities, molds, proportioning, reinforcement, surface finishes, curing, handling techniques, loading, storage, connections, and erection. Special discussion is presented covering responsibilities of structural design, handling stresses, adequacy of connections, and esthetic results. Recommended tolerances are presented. The following subjects are also discussed: (I) points and point sealants, (2) cleaning and repair, (3) glass damage, (4) surface coatings, and (5) cracking acceptability. This is the third installment of a four-part series by Committee 533; future recom-mendations will cover design of panels. [ABSTRACT FROM AUTHOR]

This Code covers the proper design and construction of buildings of reinforced concrete. It is written in such form that it may be incorporated verbatim or adopted by reference in a general building code, and earlier editions have been widely used in this manner. Among the subjects covered are: permits and drawings; inspection; specifications; materials; concrete quality; mixing and placing; formwork, embedded pipes, and construction joints; reinforcement details; analysis and design; strength and serviceability; flexural and axial loads; shear and torsion; development of reinforcement; slab systems; walls; footings; precast concrete; prestressed concrete; snells and folded plate members; strength evaluation of existing structures; and special provisions for siesmic design. The quality and testing of materials used in the construction are covered by reference to the appropriate ASTM standard specifications. Welding of reinforcement is covered by reference to the appropriate AWS standard. [ABSTRACT FROM AUTHOR]

Presents recommendations for selection and use of the following in the production of precast concrete panels: (I) portland cement; (2) back-up concrete aggregates; (3) decorative facing aggregates; (4) concrete admixtures; (5) reinforcement; (6) forming materials; (7) Jointing materials; (8) insulation; and (9) protective coatings. This is the second installment of a four-part series by Committee 533; future recommendations will cover design of panels and their fabrication; handling, and erection. [ABSTRACT FROM AUTHOR]

Outlines uses of this method of preplaced aggregate concrete construction. Discusses selection of materials and grout mix proportioning. Recommendations for form preparation, aggregate placing, arrangement of piping, grout pumping and sequence of infection, finishing, curing, and methods of quality control are made. Fundamentals of good practice in preplaced aggregate construction are recommended by which unanticipated problems can be remedied or avoided. [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 strain properties of concrete under uniaxial tensile stress are studied and factors influencing the stress-strain relation are discussed. The influence of six factors: aggregate-cement ratio, ag-gregate grading, water-cement ratio, curing con-ditions, specimen length, and loading rate are examined. The test data show that with the exception of aggregate grading, all the above factors influence to some degree the stress-strain relation of concrete under uniaxial tension. [ABSTRACT FROM AUTHOR]

The results of an extensive state-of-the-art survey are reported. Although the corrosion of pre-stressing steel is not a common problem, it has occasionally caused serious damages and failures. Corrosion of tendons is caused mostly by improper construction techniques including handling, storage and shipping, and to a lesser degree, by improper design. High quality, dense, and impervious concrete or grout can furnish permanent corrosion protection in most environments to which a highway bridge is exposed, provided that certain requirements are satisfied. Recommended corrosion preventing measures of a civil engineering character are discussed in detail. More than 100 of the most important references are used. [ABSTRACT FROM AUTHOR]

Hydrogen evolution in a heavy concrete containing ferrophosphorus aggregate was noted during construction of a biological shield for a nuclear generating station. While the reaction was of a self-limiting nature, the concrete would produce over 25 times its volume of hydrogen before the reaction ceased. The factors affecting the reaction and the possible mechanisms involved are discussed. Subsequent investigation has shown that a similar reaction occurs with ferrosilicon, another heavyweight slag, otherwise of potential value in heavy concrete. [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]

Observed data of pressure distribution on forms at an actual project are presented and discussed. A practical method of evaluating the pressure acting on prepacked concrete forms is suggested. [ABSTRACT FROM AUTHOR]

An experimental investigation was carried out to determine the resistance of popout formation in mortar. It was found that the required pressure to produce popouts on a concrete surface, from a spherically shaped particle near the surface, is directly proportional to the distance of the particle from the surface, and the tensile strength of the concrete, and inversely proportional to the size of the particle. [ABSTRACT FROM AUTHOR]

Simple formulas are presented for the prediction of fresh unit weight as well as for the relationship between cement content and mix proportions of various structural concretes. These formulas are useful mainly for proportioning structural lightweight and heavyweight concretes because the unit weight and the cement content have greater significance for these mixtures than for normal weight concretes. The formulas are also applicable when the mineral aggregate in question is blended with aggregates of differing specific gravities--such as a conventional sand and a lightweight coarse aggregate--provided that the average specific gravity of the blended aggregate Is computed by a formula developed for this purpose. Experimental results support the formulas within a wide range. The limits of validity are given. Numerical examples Illustrate the use of the formulas. [ABSTRACT FROM AUTHOR]

Presents brief introductory statement on the need for formwork standards based on the fact that 35 to 60 percent of the total cost of the concrete work in a project in the United States is in the formwork. A section is given on engineer-architect specifications noting the kind and amount of specification the engineer or architect should provide the contractor. Since the committee concludes that formwork design and engineering, as well as construction, must be the responsibility of the contractor, the recommendations contained in the report are directed to that group. However, an understanding of these recommendations by engineers and architects will aid these groups in their specification functions. The report is divided into five chapters: I. Design, 2. Construction, 3. Materials for Formwork, 4. Forms for Special Structures, and 5. Formwork for Special Methods of Construction. [ABSTRACT FROM AUTHOR]

Describes effects of replacing the fines of three structural lightweight aggregates with equal volumes of natural sand. This investigation is a con-tinuation of previous work and extends test data to broaden information about aggregates pro-duced on a sintering grate. The results illustrate improvements in both the plastic and hardened concretes. The water and cement contents required decreased with increas-ing natural sand content. Physical properties of the hardened concretes were significantly improved, though the unit weights were increased moderately. [ABSTRACT FROM AUTHOR]

Copyright of Calcified Tissue Research 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.)