Concrete Mix Proportion Research Articles

Designing concrete mixtures for strength, elastic modulus and fracture energy

There are many methods for determining a concrete mix proportion when the compressive strength is the design criterion; however, there is much less information available when other criteria, such as the fracture energy or the elastic modulus, are specified. For these cases, a new mix design nomogram has been developed from well-established concrete relationships. The application of this method is demonstrated by an experimental programme which shows the influence of cement content, water-to-cement ratio and aggregate-to-cement ratio on the compressive strength, modulus of elasticity, spliting tensile strength, fracture energy, and characteristic length of concrete. Six concrete mixtures with different water-to-cement ratios and workabilities were studied. The mix design nomogram, besides being a tool for the practitioner, can also help the researcher in selecting the most adequate mix parameters for experimental and scientific purposes. It is noted that when studying the effect of mix parameters on the properties of concrete certain constraints should be used: for instance when varying the water-to-cement ratio, the workability of fresh concrete should be kept constant and vice versa.

The Federal Outlook for High Strength Concrete Bridges

Considerable research has been conducted during the last 20 years on high strength concrete materials, mix proportions and basic properties. Some research has also been conducted during this time span on its capacity for use in bridge members. However, structural questions remain. Also, very little has been done regarding the implementation of high strength concrete bridges. This paper will document the use of high strength concrete in bridges and present bridge design concerns. Additionally, it will present significant research results and ongoing research programs, as well as highlight remaining areas for future research. It should be noted that the contents of this paper reflect the views of the authors and do not necessarily reflect the official views or policies of the Federal Highway Administration or any other federal agency.

コンクリートの破壊力学特性と寸法効果に関する実験的研究

Fracture energy has been used as a material parameter to describe the crack resistance of concrete. It is known, however, that the fracture energy depends on specimen size even if the mix proportion of concrete is the same. In this paper, the relation between the fracture properties of concrete and the micro structure, and the size effect are discussed. Three different mix proportions of concrete and three different specimen sizes are used, where the quality and the volume of coarse aggregates are kept constant. Furthermore, the applicabilities of 'size effect law' and 'two parameter fracture model' which have been noticed as potential approaches to predict the size effect of concrete structures, are discussed.

Penetration of cement paste into lightweight aggregate

Mix proportioning of lightweight concrete is generally less accurate than that of normal weight concrete. From time to time it has been speculated whether a part of the cement paste from the fresh mix also penetrates into the aggregate. This paper presents an experimental investigation on penetration of cement paste into the lightweight aggregate. During mixing of lightweigth aggregate concrete the cement paste will penetrate most of the open pores in a surface layer of the aggregate. However, a deeper penetration of silica fume particles from the cement paste was not observed. The amount of paste penetration depends on the microstructure of the surface layer of the aggregate, the particle size distribution of the cement and silica fume, and the viscosity of the paste. Since the microstructure of the surface layer may vary from one type of aggregate to another and also within the same aggregate, it may be diffcult to quantify the amount of cement paste penetrating into the aggregate. In addition to water absorption, penetration of cement paste further adds up to the unaccuracy in the mix design of lightweight aggregate concrete.

Fracture and Failure of Concrete in Uniaxial and Biaxial Loading

General analytical equations are developed to predict the overall failure stresses for plain concrete subjected to biaxial stresses. Specifically, failure equations are derived for uniaxial tension, uniaxial compression, biaxial tension, biaxial compression‐tension, and biaxial compression. The general framework of the proposed model is based on the actual events that occur in the material during loading. According to previous experimental investigations, internal microcracks exist in the concrete prior to the application of any external loading. It is shown that the growth and interaction of these preexisting microcracks in the mesostructure of the concrete eventually cause the macroscopic failure of the specimen. Only experimental parameters (concrete mix proportions and coarse aggregate sieve gradation) are required to predict any of the failure stresses. The results generated from the models compare favorably to the experimental data for all loading cases, even though the formulation is not adorned with any unidentifiable constants or parameters.

Compression creep behaviour of steel fibre reinforced cement composites

The paper presents the results of an experimental investigation to determine the influence of steel fibre reinforcement on the creep of cement matrices under compression. Creep tests were carried out at a number of applied stress-strength ratios ranging between 0.3 to 0.9. Melt extract and hooked steel fibres were used at volume fractions ranging between 0 and 3% by volume of a mix. Three types of cement matrices were used namely cement paste, mortar and two mix proportions of concrete.

Fiber Reinforced Beams Under Moment and Shear

The science and technique of reinforcing Portland cement concrete by incorporating fibers is now well established through research and practice. However, studies on steel fiber reinforced concrete elements have been devoted primarily to observations under unit actions. The present report gives the results of thirty plain and fiber reinforced concrete beams, the majority of which are tested under combined actions of moment and shear. The principal variables are the concrete mix proportion, fiber volume fraction and shear span.

On the Correlation of Consistency and Strength of Concrete to the Attrition Rate of Fine Aggregate

AbstractOn the basis of experimental studies correlations were found between attrition rate of fine aggregates on one hand and consistency of fresh concrete and compressive strength of hardened concretes on the other. For fine aggregates complying with standard requirements, differences of up to 15 MPa (2100 psi) in compressive strength were observed between concretes made with high and low quality fine aggregates when other factors are essentially identical. For identical concrete mix proportions slump values between 190 and 0 mm (7.6 and 0 in.) were observed.

The characteristic water of aggregate testing and applications

The paper presents a new quality characteristic of aggregate the characteristic water (CW): a method to determine it and two of its applications: to the control of the quality of aggregate and to the mix proportioning of concrete. The CW represents “the amount of water resulting from a standard test, which covers the surface of the particles and partially satisfies their absorption”. The CW is proportional to the specific surface and is taking into account size, shape, texture and immediate water absorption of aggregate. The method used to determine CW is carried out on a significant sample of 5kg aggregate, using a simple and robust device. The reliability of the method has proved very satisfactory.

Investigation of the absorption of water by lightweight aggregate from cement paste

The change of workability of lightweight concrete after mixing indicated a movement of water in the fresh concrete. The small alteration of concrete strength caused by major changes in water/cement-ratio (ω) may also be partly affected by the ω-value in the hardened paste, which is not as designed. Some tests on the water absorption by the aggregate from the cement paste show that the addition to the mix of the water absorbed in 30 min (W 30) is no guarantee that the water/cement-ratio in the cement paste is as planned in mix design. The water absorption of the porous aggregate is primarily governed by porosity and pore structure, in a cement paste it is affected additionally by the water requirement of the paste, i.e. its water/cement-ratio ω, and the amount of matrix in the concrete mix proportions. To obtain appropriate information on workability and strength development, preliminary tests have to be made taking account of the mix procedure, the time when adding water and the amount of water added.

Contractors and Production of Durable Air-Entrained Concrete

The contractor-modification of air-entrained concrete mix proportions and production practices to suit actual construction conditions is covered in detail. The effects of alternate mix materials, materials proportions, and mixing practices on air entrainment characteristics and concrete durability are outlined. The effects of conventional, accelerated, and extreme curing practices on concrete durability are reviewed. The selection and implementation of quality control tests for air-entrained concrete is covered.

Voraussage der verformungs- und festigkeitseigenschaften von beton unter dauerlast

Using existing experimental data and statistical methods, the influence of different factors on the creep development and ultimate creep strain is analysed. Both linear and non-linear creep are investigated. It is shown that the creep behaviour of normal weight concrete can be reliably predicted for design when instead of traditional parameters of concrete mix proportion the standard concrete strength and the water content in concrete mix are used. The decrease of strength of concrete under high sustained load can also be predicted using fracture mechanics methods and statistical estimation of linear creep strain.

Vibrating Compaction of Road AE-Concrete by Surface Vibrator

This paper describes the compaction of AE-concrete pavement having 30cm in depth by a surface vibrator.The test results are summarized as follows:(1) It is possible to consolidate AE-concrete having 30cm in depth with a surface vibrator by choosing the optimum vibrating condition for each mix proportion of concrete.(2) The optimum condition of compaction by a surface vibrator seems to have good correlation with the settlement time measured by the consistency test with a vibrator used for road concrete.(3) As the optimum condition, the frequency of 7000vpm and the acceleration of 20g are found to be suitable for the concrete having the settlement time of 25sec., the frequency of 5000vpm and the acceleration of 15g for the one with the settlement time of 15sec., and the acceleration of more than 5g and the amplitude of 0.6 to 1.4mm for the one with the settlement time below 10sec.

Concrete optimized mix proportioning (COMP) a reply to the discussion by V.M. Malhotra

Concrete optimized mix proportioning (COMP) a reply to the discussion by V.M. Malhotra

Pumping Lightweight Aggregate Concrete

In Japan the pumping of concrete is generally in practice in the building projects to save labor because of manpower shortage in the country. But there are some problems in pumping the concrete, especially of the lightweight aggregate concrete.It is the aim of this report to present information on the above mentioned problems which has been obtained through the investigations into the practices adopted in several projects.The summaries are as follows:(1) The mix proportion of concrete is revised to some degree to make the pumping easier, although there has not yet been found a general standard.(2) In many cases, the water requirement in concrete mix is increased from 5 to 10kg per cubic meter of concrete and also is the fine/combined aggregate ratio increased from 3 to 5%.(3) The mix proportion of cement paste in concrete which is pumped up to comparatively high places (e. g. higher than 20m) has tendency to be increased.(4) By receiving high pressure during the pumping process, the lightweight aggregate absorbs much more water than when it is under atmospheric pressure, therefore, the workability of concrete becomes lower than what it was before the pumping. The decrease of slump is in many cases not more than 3cm but in some cases exceeds 10cm.(5) The entrained air increases or decreases, as the case may be, but the variation shows in many cases not more than 1%.(6) The compressive strength of concrete is also affected by pumping. In certain circumstances, there is decrease of strength, even at times at the rate of more than 10%. This phenomenon may be ascribed, though not thoroughly analyzed yet, to the water which has found its way into the lightweight aggregates during the process of the pumping, due to its pressure, and which oozes out into the bond between the aggregate and the cement paste and damages it, after the concrete is moulded.(7) Thorough irrigation of the aggregates in stock yard is effective in decreasing the amount of water to be pumped into the lightweight aggregates.

Bearing Capacity of Lightweight Aggregate Concrete

The present paper describes the results of the experimental and theoretical investigations made on the bearing capacity of lightweight aggregate concrete. Laboratory tests were conducted to clarify the effects of the dimension of the specimen, the ratio of footing area to loading area of the specimen and concrete mix proportion on the bearing capacity of the cylindrical concrete specimen, which was loaded to be subjected to circular pressure at the center of the top and supported by the entire surface at the bottom. The similar loading tests were also carried out on normal concrete. From this test, the following conclusions were obtained:(1) The bearing capacity (σu) was nearly proportional to compressive strength (σc) ranging from 200 to 400kg/cm2 for normal concrete, but σu was not proportional to σc for lightweight concrete. The ratio of the bearing capacity of lightweight concrete to that of normal concrete were about 1.0, 0.85 and 0.70 when the compressive strength was about 200, 300 and 400kg/cm2, respectively.(2) It is found, therefore, that the coefficients included in conventional empirical formulas to determine the bearing capacity of lightweight concrete should be varied in accordance with the change of concrete strength.(3) The results showed that there was no obvious difference due to the influencing factors, except concrete strength, between the normal and the lightweight aggregate concrete. Moreover, the characteristics of the approximate theoretical solution derived by the author were disccused and compared with the test results obtained and the solutions proposed by other researchers.

1052 人工軽量骨材を用いたコンクリートのコンシステンシーと調合に関する研究(材料・施工)

1052 人工軽量骨材を用いたコンクリートのコンシステンシーと調合に関する研究(材料・施工)

Rationlization of the Trial Mix Approach to Concrete Mix Proportioning and Concrete Control Therefrom

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Experimental Studies on Fluidity of Grouting Paste for Prestressed Concrete

The qualities necessary for the grouting paste for prestressed concrete are faculty of smooth flow, little bleeding and change of volume, high strength (compressive and bond) and resisting power for freezing. But those qualties, excepting the faculty of flow, are improved by the minimum use of water.The current apparatus for measurement of fluidity of grouting paste are such as shown in Fig. 1∼Fig. 3, either of which is used, according to the enquête undertook by the Dutch Grouting Committee, in various foreign countries except in Holland.The“International Recommendation”arranged by the same Committee has recently stated that“The water-cement-ratio must be as low as possible for a good workability. The fluidity of the grout may be measured with every kind of apparatus that gives reproducible results. Every type of apparatus must be calibrated in poises.”But no apparatus has been calibrated in poise so far.It is partly due to the thixotropic property of cement paste but mainly to the assumption that cement paste is nothing but a Newtonian liquid. The experiments which the writers have made with his coworkers on an assumption that cement paste is Bingham body clearly show that the measurements done with those apparatus can be expressed in terms of absolute unit.The measurement has been done by means of BH type rotation viscometer (Photo. 1) at various rates of shear, that is, its number of rotation of rotor.Investigation has also been made as to the change which the charactaristic values of ηpl and ν undergo by taking into consideration various conditions necessary for the presstressed concrete grouting, that is, mix proportion, types and numbers of rotation of mixer, mixing time and the fineness of cement.Several results are shown in the following figures. From these experiments some conclusions have been obtained as follows:(1) Cement paste behaves as Bingham body, and the fluidity of grouting paste is represented both by ηpl and ν.(2) The values of these rheological properties are influenced by mixproportion, types and numbers of rotation of mixer, mixing time and the fineness of cement etc..(3) The current apparatus for measurement of fiuidity of paste which are shown in Fig. 1∼ Fig. 3 will not be sufficient for measurement of ηpl and ν.

General relation between mix proportion and cement content of concrete

Summary Semi-empirical equations are presented for the relation between cement content and mix proportion of concrete. Other variables are the consistence, specific gravities of cement and mineral aggregates, grading of aggregate, and air content. The paper shows equations for the case in which only one material is used as mineral aggregate (equations 1–4), and for the more general case in which a blend of two materials is used (equations 5–8). The form of the equations is relatively simple considering the large number of variables involved. The values calculated from the equations are compared with results of experiments performed by various research workers, and it is shown that there is good agreement between calculated and experimental values.