Early Strength Of Concrete Research Articles

The Effect of Accelerators and Mix Constituents on the High Early Strength Concrete Properties

The present research study focused on the high early strength concrete properties that can be produced with large replacement of cement by fly ash. Also, the effects of adding fibres on the compressive strength gain and early age strength gain properties are determined. Tests were conducted on different high strength concrete specimens, where fly ash was substituted for cement up to 50%. Different types of concrete specimens were casted and tested for different fine-to-coarse aggregate ratio, metallic fibre content, cement-to-total-aggregate ratio, and accelerator dosage. The test results indicated that high early strength concrete (50.7 MPa at 7 days) was obtained for higher F/C ratio of 0.8, C/TA ratio of 0.24, and higher dosage level of steel fibre at 1.5%.

On early Mechanical Properties of Artificial Sand Concrete

This paper studies the early mechanical properties of artificial sand concrete, we found by comparison with natural sand concrete that the slump of artificial sand concrete were increased by 85%, and the strength 0f 16h and 1d and3d were increased by 23.4% and 20% and 11%. Therefore, artificial sand can significantly improve the workability of concrete mix, improve the early strength of concrete. It has guidance significance to the early strength of concrete engineering.

Experimental Analysis of Relationship between Pore-Structure and Frost-Resistance of Concrete

The influence of admixture on concrete pore structure was analyzed by using the mercury intrusion method and the rapid frozen-thaw method under the condition of the same water/binder ratio in this paper, and thus the relationship between pore structure and frost resistance of concrete were analyzed. When the compound mineral ad-mixture is mixed, the porosity rate of concrete can be decreased and the harmful hole is in-creased, the less-harm hole and the no-harmful hole are decreased. The early strength of concrete is not decreased. But the strength has the increasing trend in the late, which is more favorable for the impermeability and corrosion resistance. But the improvement of the freezing resistance is not obvious. The admixture of air entraining agent can increase the porosity and more-harmful hole, and the concrete strength will be decreased, which will be not favorable for the freezing resistance of concrete. If these two substances are admixed at the same time, the concrete porosity is increased, and the pore size distribution of concrete can be reasonable. The decrement of concrete strength is not obvious, but it is favorable for the freezing resistance of concrete.

Development of an Economical High Early Strength Concrete Mix for Paving of Provincial Roads in Sri Lanka

Rigid pavement construction has a long history. Ready mixed or site mixed or site mixed concrete is used for rigid pavement construction. However, conventional concrete mixtures require more than 7 days to gain adequate strength to allow for traffic. Development of high early strength concrete would be a solution to allow traffic within a reasonable time. However, use of high cement content in early strength concrete induces distress in the pavements and would not be an economical mix. A high performance concrete mix was developed for rigid pavement construction using a low cost admixture with available material in Sri Lanka. Study has shown that 3% of commercial grade CaCl2 can be used as an accelerator to obtain required compressive strength and the flexural strength of concrete in 12 hours. Strength gain was verified by the maturity test conducted for a slab placed under field condition. Slab temperature was also measured with time and found temperature rise due to hydration was insignificant. Using the mix proportion developed, concrete roads can be allowed for traffic in 12 hours and can also be used for repair works of the existing roads. Life cycle cost analysis was performed taking into account the construction cost, maintence cost and the user cost. The study has shown that there is 26% saving by using high early strength concrete developed in this study.

Experimental Study on Improving the early Strength of Fly Ash Concrete

This manuscript makes experiments on the macroscopic concrete strength improvement of fly ash activation at early age. At the same time we test the microstructure of fly-ash waste residue concrete cementious materials and calculus, analyzing HPC preliminary mechanism tentatively. The mechanism of improving the early concrete strength by fly ash activation is expatiated, which improves activation mechanism and technology of fly ash.

Properties of fly ash concrete modified with hydrated lime and silica fume

This paper presents the results of an experimental investigation on the properties of fly ash concrete incorporating either hydrated lime or silica fume to improve the early strength of concrete. Test results indicated that the addition of lime and silica fume improved the early age compressive strength of fly ash concrete. The inclusion of silica fume was also found to increase the 28 days strength significantly. The air permeability of concrete containing lime and silica fume either decreased or remained almost the same when compared to the concrete without these. The addition of lime and silica fume also improved the sorptivity of concrete. Through the use of differential scanning calorimetry and thermogravimetric analysis (DSC/TG), it was demonstrated that the addition of hydrated lime increased the Ca(OH) 2 content; whereas the addition of silica fume decreased the Ca(OH) 2 content in the cement paste. The mercury intrusion porosimetry (MIP) data confirmed the beneficial action of hydrated lime and silica fume, towards decreasing the total pore volume of fly ash cement paste.

Assessment of methods for optimising ternary blended concrete containing metakaolin

The relative effectiveness of three approaches—isothermal calorimetry, trial batching and particle packing models—for optimising mix proportions in Portland cement/metakaolin (MK)/fly ash (FA) ternary blended concretes was compared through measurements of workability and compressive strength, in consideration of economy. Mixtures were prepared using single cement and class C FA and two MKs of varying fineness. The finer MK showed a higher rate of reaction, but the isothermal calorimetry also suggested that MK replacements of 5% or higher are needed to overcome the hydration delay resulting from the use of 25% by mass FA. Trial batches at three water-to-cementitious materials ratios (w/cm)—0·30, 0·40 and 0·50—were designed based on the calorimetry results. While workability decreased with increasing MK content, similar or better workability than the control mixes was achieved in the ternary blends. The compressive strength significantly increased with increasing MK content, as compared to the ordinary concrete and the FA binary blends, and especially at low w/cm (i.e. w/cm = 0·30). The trial batch strength results confirmed that the hydration rates (measured by isothermal calorimetry) could be used to optimise binder composition for early concrete strength. However, in the third approach, the particle packing model was found to be insufficiently related to measured 1-day strength or to strength in higher w/cm concrete; the closest relationship between the primary model parameter (q) and strength was found at lower w/cm and at later ages (i.e. 28 days). It is proposed that the lack of consideration of the constituent's chemical reactivity of highly reactive materials, such as MK, makes this approach unreliable at early ages and at higher w/cm. Finally, despite the lack of correlation between q and strength, results show q values of 0·26-0·29 are optimal for workability.

Preliminary Study for Strength and Freeze-Thaw Durability of Microwave- and Steam-Cured Concrete

This study investigates the effects of steam and microwave curing on the strength development and freeze-thaw durability of concrete. Two steam-curing treatments, four microwave curing times and four types of concrete mix, were used in this study. The test results indicated that microwave heating could further increase the early strength of concrete. Pozzolanic reaction of silica fume, fly ash, and blast-furnace slag was observed to be further promoted by steam-microwave curing. Concrete samples with 10% silica fume added responded well to microwave curing. The strength gain development of concrete appeared to level off after 40 min of microwave curing. Thus, a 40-min microwave heating time appeared to be the optimal curing time. The microwave-cured concrete did not show an increase in deterioration relative to the concrete that was steam cured, but showed an increase in strength. The strength of the top layer of the steam-cured concrete blocks is lower than the strength of the middle or bottom layer.

A Very Early Strength Concrete for Highway Construction

Abstract The purpose of this research study was to develop an improved very early strength (VES) concrete mix for highway construction. More than 50 concrete mixes were evaluated for strength, shrinkage, and curing rate (maturity), eventually leading to the development of an optimized VES concrete mix with improved performance characteristics. The new mix, which is detailed in the paper, can gain strength more reliably than the former standard New Jersey Department of Transportation (NJDOT) VES mix, reaching a flexural strength of 350 psi (2.4 MPa) in less than 6.5 h. The improved mix also exhibited 79 to 93 % less shrinkage. The study found that maintaining an initial mix temperature of 28°C (82°F) is crucial to attain target strengths.

혼화재 종류 및 치환율에 따른 모르터의 조기강도 특성에 관한 연구

Recently, due to the increase of high-rise buildings construction, many researches for making harden of concrete earlier and remove of forms faster are being performed to reduce construction period. In this study, we compared and analysed the early strength properties of mortar according to the kinds and replacement ratio of mineral admixture to select the kinds and replacement ratio of mineral admixture of high early strength concrete. For this purpose, mortar mixtures according to the kinds(FA, MK, ZR, BFS, DM) and replacement ratio(0, 2, 4% by volume of sand) of mineral admixture were selected. From our test data, early-age compressive strength decreased in accordance with the increase of replacement ratio of fly-ash(FA) & blast furnace slag powder(BSF) and, in case of addition admixture, early-age compressive strength of with containing 4% appeared higher compared with containing 2%.

폴리카르본산계 조강혼화제 혼합 콘크리트의 강도 및 내구 특성

This study reports the properties of high early strength & durability of concrete using PC admixture. To apply these data to construction site, we did the lab tests. The target of this study is to accomplish early strength of concrete (5.0 Mpa/18 hr), and we did the durability tests such as length change test, chloride ion penetration test, fleeting and thawing test, adiabatic test, etc. And we tested the porperties of concrete by the different factors, such as the type of admixtures, curing temperature, the amount of binder, etc. Through the test of concrete using the different type of admixture, PC type was more excellent than PNS type admixture. As a result, we made a concrete of high early strength concrete, and excellent durable concrete. According to these tests, we concluded that we can apply this type of PC admixture to the civil & construction site, and we can reduce the term of works and finally we will accomplish the economical construction.

Effect of Finely Ground Calcium Hydroxide on the Strength Development of Steam-Cured Concrete

In order to enable concrete production plants to reduce their manufacturing processes and costs, we prepared concrete with finely ground Ca(OH)2, which improves the setting of concrete. We steam-cured concrete, and experimentally evaluated the effects of the added Ca(OH)2 and the curing conditions on the concrete's strength development. The results show that adding finely ground Ca(OH)2 enhances the early strength of concrete. At a maximum temperature of 80°C the concrete exhibited the same level of strength as concrete that had been cured for 24 hours before removing the mold, even though a shorter curing time was used.

Effect of Confining Pressure on Modeling High Early Strength Concrete under Uniaxial Loading

Better understanding of concrete behavior is beneficial to the determination of concrete strength and detection of cracking using nondestructive testing techniques such as ultrasonic and acoustic emission. For advanced nondestructive evaluation of high early strength concrete under triaxial compression loading, stress-strain relationship in axial as well as in radial directions needs to be described in explicit form. This paper presents empirical models developed for high early strength concrete under active confinement to explore the effect of confining pressure. Empirical model for axial stress-strain relationship is determined first. Transverse deformation model is automatically generated from the given axial stress-strain model using plastic strain rate. Parameters used in the model are identified and their recommended values are provided. Compressive strength of 24 MPa and 45 MPa concretes are considered along with four different levels of confining pressures.

Resistance to Freezing and Thawing Cycles and Scaling Resistance of Very High Early Strength Concrete

Abstract A very high early strength portland cement-based concrete (VHES) is used to prevent long closures of highway lanes by completing any necessary repairs overnight. This technology has been embraced by several DOT agencies, including those in areas where the concrete will be subjected to freezing and thawing cycles. Flexural strength of VHES concrete is the critical parameter to permit traffic flow without damage to the concrete. It is possible to produce air-entrained rapid repair concrete, but this places higher requirements on the mixture proportions to overcome strength reduction caused by the presence of air. This article presents data showing that it is possible to attain the necessary strength and achieve adequate resistance to freezing and thawing cycles. The evidence presented includes accelerated testing using ASTM C 666, Procedure A, and scaling resistance using ASTM C 672. Additional evidence is presented showing that VHES concrete of low w/c can be durable with larger than acceptable spacing factor levels or without air entrainment.

STRENGTH PROPERTIES OF ULTRA HIGH EARLY STRENGTH STEEL FIBER REINFORCED ROLLER COMPACTED CONCRETE FOR PAVEMENTS

This report discuss about early age strength of ultra high early strength steel fiber reinforced roller compacted concrete which were combined ultra high early strength concrete and steel fiber reinforced roller compacted concrete. The consistency of ultra high early strength steel fiber reinforced roller compacted concrete and standard roller compacted concrete are equivalent. As for the curing time which reaches mix strength is shortened by 1/6-1/9 as compared with standard RCCP. We clarified early age strength for ultra high early strength steel fiber reinforced roller compacted concrete as compared with ultra high early strength steel fiber reinforced concrete with slump.

Increasing Coal Fly Ash Use in Cement and Concrete Through Chemical Activation of Reactivity of Fly Ash

Nearly 60% of the electricity in the USA is produced by coal-fired plants, which results in the production of a large quantity of coal combustion residues, among which coal fly ash is the major component. Many applications have been developed for coal fly ash. The use of coal fly ash as a cement replacement in concrete is the most attractive one because of its high volume utilization and widespread construction. However, the replacement of cement with coal fly ash in Portland cement concrete usually increases the setting time and decreases the early strength of concrete. The addition of chemical activators such as Na2SO4 or CaCl2 accelerates pozzolanic reactions and changes pozzlanic reaction mechanisms between fly ash and lime, which results in decreased setting time, accelerated strength development, and increased strength of materials containing fly ash, especially with a high percentage of fly ash. The other promising cements include alkali-activated fly ash and alkali-activated fly ash-ground blast furnace slag cements, which can exhibit very high strength in the presence of proper alkaline activators. Thus chemical activation of reactivity of fly ash is an effective method to increase the use of fly ash in concrete.

Rehabilitation of Ellaville Weigh Station with Ultrathin Whitetopping

The Florida Department of Transportation constructed the first ultrathin whitetopping (UTW) project at the Ellaville truck weigh station on I-10 in northwest Florida. This rehabilitation project included the placement of UTW on the existing asphalt pavement, which had experienced severe rutting problems. Layer thicknesses for the UTW were 80 mm and 100 mm. The joint spacings for the UTW panels were 1.2 m and 1.6 m. High early strength concrete was used in this project. Polypropylene fibers were included in the concrete for the sections on the west side of the weight platform and plain concrete was used on the east sections. The joints on the east section were sealed with silicone sealant and the joints on the west section were left unsealed. Falling weight deflectometer tests and frequent condition surveys were performed on the projects. After 1 year of service and 1.1 million equivalent single-axle loads, the UTW shows good performance. Success and long-term performance of the UTW is highly dependent on the degree of bonding between the UTW and the asphalt base. During the study period, panels 1.2 m2 and 1.6 m2, concrete with and without fibers, sealed and unsealed joints, showed similar performance. It is predicted that the 1-year performance of the UTW at the weigh station is equivalent to 4.5 years of service at a medium traffic intersection.

Evaluation of early concrete strength

With a view to verifying the feasibility of evaluating early concrete strength, an extensive experimental program was developed for testing the strength of steam-cured 8 cm concrete cubes after 17 hours (Ra) and comparing the results with the strength of 15 cm cubes at 28 days (Rs). The relationship of Ra to Rs depends on the steam curing cycle, on the maximum aggregate size and its influence in relation to sample size, and on the rate of loading during the test. The Ra-Rs regression line was calculated for different concrete mixes using various types of cement (to Italian standards), i.e., Portland 325 and 425, pozzolana 325 with fly ash and Portland 325 with a superplasticizing admixture. A linear relationship generally proved reliable as Rs=mRa+c, where m and c are constants depending on the type of cement, the curing cycle and the maximum aggregate size. The coefficient of variation was about 4–5%, reaching 6% when all concrete mixes tested were considered.

建設材料特集 蒸気養生過程で発生する鉄筋コンクリート部材の微細ひび割れ性状

Atmospheric pressure steam curing has been widely used for precast concrete products, as the high curing temperature accelerates early concrete strength development. Though steam curing has an economic advantage over ordinary moist curing, it has one problem that should not be ignored. Sometimes fine cracks are formed on the surface of precast concrete products. It has been proposed that these fine cracks are formed during a certain stage of steam curing. The purpose of this investigation was to reveal the condition and mechanism of fine crack formation on the surface of steam cured concrete. A new X-ray technique, using a contrast medium, was developed and used to detect fine cracks on the surface of concrete. As a result of the study, three different types of fine cracks, namely mortar cracks, vapor cracks and separation cracks between aggregates and pastes were observed. They occurred at different stages of steam curing. The condition of developing cracks was also studied and compared with the standard specification of the Japan Society of Civil Engineers.

A simple pull-out test for in situ determination of early strength of concrete

The aim of the work reported was to develop a simple non-destructive testing method for monitoring strength development between 5 MPa and 15 MPa for form stripping in industrialized building. Existing test methods are briefy reviewed and requirements for the test summarized. A simple pull-out test has been developed using wood-screws, which can be inserted in critical areas of the element during casting. In a laboratory investigation the deflect of different variables on the pull-out load-standard cube strength relationship was examined. These included cement content, water/cement ratio, slump, mode of compaction and accelerated heat curing. Evaluation of test results indicates low dependence of the proposed method on mix proportions, and suggests reasonable repeatability. Further tests are proposed to refine the method for various field applications.