Sand-aggregate Ratio Research Articles

Chloride diffusion in alkali-activated fly ash/slag concretes: Role of slag content, water/binder ratio, alkali content and sand-aggregate ratio

The widespread application of alkali-activated fly ash/slag (AAFS) concrete requires the satisfaction of a series of performance criteria both from its early age properties (e.g. workability, strength) and long-term stability. In this study, long-term (till 180 days) natural chloride diffusion tests were conducted to evaluate the chloride diffusion in AAFS concretes prepared with different slag content, water/binder (w/b) ratio, alkali content, and sand-aggregate ratio. The results revealed that AAFS concretes obtained in this study were generally regarded as flow/high flow concretes (slump > 100 mm) with compressive strength > 50 MPa at 28 day. The free chloride diffusion coefficient (Df) of AAFS concretes was between 0.4 and 1.8 × 10-12 m2/s. The slag content and w/b were found as dominant parameters affecting the long-term chloride transport in AAFS concretes, while the sand-aggregate ratio presented a limited effect. The formation of more C-A-S-H gels (by increasing slag content ≥ 50%), and lower w/b (≤0.45) at Na2O content of ∼ 5% was preferred for AAFS concretes with good workability, strength and durability. MIP results indicated that capillary pores in AAFS reached percolation and became disconnected after 180 days. The long-term chloride diffusivity of AAFS concretes was closely related to the threshold pore diameter and volume of pores > 5 nm. The more larger pores, the higher chloride diffusion coefficient was.

Application of plastic concrete cut-off wall in reinforcement of reservoir

Plastic concrete is a kind of suitable material for cut-off wall of earth dam, which has low elastic modulus and permeability, large ultimate deformation, and good workability. In this paper, the mix proportion of plastic concrete with 50% bentonite content, water-binder ratio of 1.00 and sand-aggregate ratio of 55% is proposed, and the plastic concrete cut-off wall has been successfully applied to the reinforcement project of Huizhou Zengbo Lianhe reservoir. All the indexes meet the design requirements. The seepage of the main dam was reduced by 67%, and the piezometric level behind the wall was reduced by 6-9 m.

Modeling compressive strength of recycled aggregate concrete by Artificial Neural Network, Model Tree and Non-linear Regression

Abstract In the recent past Artificial Neural Networks (ANN) have emerged out as a promising technique for predicting compressive strength of concrete. In the present study back propagation was used to predict the 28 day compressive strength of recycled aggregate concrete (RAC) along with two other data driven techniques namely Model Tree (MT) and Non-linear Regression (NLR). Recycled aggregate is the current need of the hour owing to its environmental friendly aspect of re-use of the construction waste. The study observed that, prediction of 28 day compressive strength of RAC was done better by ANN than NLR and MT. The input parameters were cubic meter proportions of Cement, Natural fine aggregate, Natural coarse Aggregates, recycled aggregates, Admixture and Water (also called as raw data). The study also concluded that ANN performs better when non-dimensional parameters like Sand–Aggregate ratio, Water–total materials ratio, Aggregate–Cement ratio, Water–Cement ratio and Replacement ratio of natural aggregates by recycled aggregates, were used as additional input parameters. Study of each network developed using raw data and each non dimensional parameter facilitated in studying the impact of each parameter on the performance of the models developed using ANN, MT and NLR as well as performance of the ANN models developed with limited number of inputs. The results indicate that ANN learn from the examples and grasp the fundamental domain rules governing strength of concrete.

지하식 LNG 저장탱크의 지붕 콘크리트의 요구성능에 관한 실험적 연구

이 연구는 200000 m³의 용량을 갖는 지하식 LNG 저장탱크의 지붕 콘크리트에 대한 요구성능 및 이에 따른 콘크리트의 최적배합비를 도출하고, 현장시공의 자료로 제안하기 위한 것이다. 지붕 콘크리트는 돔형 지붕의 경사기울기에 따라 굳지 않은 콘크리트의 시공성 및 충전성이 요구된다. 또한, 1.4~0.6 m의 지붕두께를 고려한 수화열 저감과 콘크리트 타설 후의 프리스트레싱 작업 및 air support의 제거공정에 따른 단계별 압축강도의 확보가 중요한 요구성능이다. 이러한 조건을 고려하여 지붕의 기울기가 20° 미만일 경우에는 슬럼프 100±25 mm, 20° 이상일 경우에는 150±25 mm로 선정하였으며, 경시변화 60분을 만족해야 한다. 특히, 91일 재령의 설계기준강도 30 MPa, 프리스트레싱 작업시 7일 재령의 압축강도 10 MPa, air support 제거공정에서 21일 재령의 압축강도 14 MPa을 만족해야 한다. 석회석 미분말의 최적 치환율은 구속시험 결과에 따라 정하였으며, 주요 배합변수는 물-시멘트비, 잔골재율 및 고성능 AE감수제의 첨가율 등이다. 배합시험 결과, 저열 포틀랜드 시멘트 및 석회석 미분말을 사용한 지붕 콘크리트의 최적배합 조건은 석회석 미분말의 최적 치환율 25%(내할), 물-시멘트비 57.8%, 잔골재율 42.0%로 나타났으며, 공기량 및 슬럼프의 시험결과도 경시변화 60분까지 성능을 만족하였다. 또한, 단열온도 상승시험의 결과, 단열온도 상승양(Ｑ∞)이 26.3℃, 상승속도(γ) 0.58로 선행탱크(TK-13,14)와 비교해 볼 때 매우 낮게 나타나 수화열 저감의 효과를 기대할 수 있다. 이러한 요구성능 및 최적배합 조건을 만족하는 설계기준강도 30 MPa(배합강도 36 MPa)의 지하식 LNG 저장탱크의 지붕 콘크리트용으로 제안하였다.

Study on Shrinkage Deformation of High Flexural Strength Concrete at Early Age

Shrinkage deformation of concrete in early age, which mainly varies with factors such as cement quantity, bonder type, air content and sand aggregate ratio, was studied. Test species, which sizes are 100 mm×100 mm×515 mm, were put into temperature and humidity controlled box. Value of shrinkage deformation in different humidity was recorded by micrometer gauge. Humidity will vary automatically with need in (20±1)°C temperature level in the box. Humidity increases from current value to 99 percent in 30 minutes. Initial value of shrinkage deformation should be achieved after 180 minutes with humidity of 99 percent. Then humidity decreases from 99 percent to 10 percent in 30 minutes. Value of shrinkage deformation should be achieved after 180 minutes with humidity of 10 percent. It will experience three loops around. It is shown that: (1) early age shrinkage deformation of cement concrete is enlarged with increasing cement quantity; (2) early age shrinkage deformation of high flexural strength concrete (HFSC) with pure silica is larger than those with fly ash and silica and those with pure fly ash. The late two are almost with the same shrinkage deformation; (3) early age shrinkage deformation of HSFC is enlarged with increasing air content at 3 days age; (4) after 28 days age, early age shrinkage deformation of HSFC is reduced with increasing air content when it is below 6.8 percent and it will enlarge with air content when above 10 percent.

지하연속벽용 병용계 고유동 콘크리트의 시공 품질 및 보증강도 평가에 관한 연구

The primary purpose of this study is to estimate the guaranteed strength and construction quality of the combined high flowing concrete which is used in the slurry wall of underground LNG storage tank. The required compressive strength of this type of concrete become generally known as a non economical value because it is applied the high addition factor for variation coefficients and low reduction factor under water concrete. Therefore, after estimation of the construction quality and guaranteed strength in actual site work, this study is to propose a suitable equation to calculate the required compressive strength in order to improve its difference. Application results in actual site work are shown as followings. The optimum nix design proportion is selected that has water-cement ratio 51%, sand-aggregate ratio 48.8%, and replacement ratio 42.6% of lime stone powder by cement weight. Test results of slump flow as construction quality give average . 500mm flowing time and air content are satisfied with specifications in the rage of 6.3 seconds and 4.0% respectively. Results of strength test by standard curing mold show that average compressive strength is 49.9MPa, standard deviation and variation coefficients are low as 1.66MPa and 3.36%. Also test results by cored cylinder show that average compressive strength is 66.4MPa, standard deviation and variation coefficients are low as 3.64MPa and 5.48%. The guaranteed strength ratio between standard curing mold and cored cylinder show 1.23 and 1.32 in the flanks. It is shown that applied addition factor for variation coefficients and reduction factor under water concrete to calculate the required compressive strength is proved very conservative. Therefore, based on these results, it is proposed new equation having variation coefficients 7%, addition factor 1.13 and reduction factor 0.98 under water connote.

Investigation of the mix ratio design of lightweight aggregate concrete

According to the analysis of the domestic and overseas researches and achievements of lightweight aggregate concrete, a new strength formula on account of tube compressive strength of lightweight aggregate and glue–capacity ratio is put forward on the mix ratio design of lightweight aggregate concrete. The conception of concrete filler coefficient is also proposed, the theoretical formula of sand–aggregate ratio is deduced and the quasi-principle of stationary water consumption by considering the working character of concrete is summarized. Therefore, the designing equation of mix ratio of lightweight aggregate concrete which is tested by some further experiments is defined.

A prediction on mix proportion factor and strength of concrete using neural network

An artificial neural network was applied to predict compressive strength, slump value and mix proportion of a concrete. Standard mixed tables were trained and estimated, and the results were compared with those of the experiments. To consider variabilities of material properties, the standard mixed tables from two companies of Ready Mixed Concrete were used. And they were trained with the neural network. In this paper, standard back propagation network was used. The mix proportion factors such as water cement ratio, sand aggregate ratio, unit water, unit cement, unit weight of sand, unit weight of crushed sand, unit coarse aggregate and air entraining admixture were used. For the arrangement on the approval of prediction of mix proportion factor, the standard compressive strength of 180 kgf/cm2∼300 kgf/cm2, and target slump value of 8 cm, 15 cm were used. For the arrangement on the approval of prediction of compressive strength and slump value, the standard compressive strength of 210 kgf/cm2∼240 kgf/cm2, and target slump value of 12 cm and 15 cm were used because these ranges are most frequently used. In results, in the prediction of mix proportion factor, for all of the water cement ratio, sand aggregate ratio, unit water, unit cement, unit weight of sand, unit weight of crushed sand, unit coarse aggregate, air entraining admixture, the predicted values and the values of standard mixed tables were almost the same within the target error of 0.10 and 0.05, regardless of two companies. And in the prediction of compressive strength and slump value, the predicted values were converged well to the values of standard mixed tables within the target error of 0.10, 0.05, 0.001. Finally artificial neural network is successfully applied to the prediction of concrete mixture and compressive strength.

압축강도에 따른 수중불분리 콘크리트의 배합설계에 관한 연구

At present, the antiwashout underwater concretes are used as popular construction materials in European countries, the United States and Japan. The water-soluble polymers in the antiwashout underwater concretes provide excellent segregation or washout resistance, self-compaction and self-leveling property to the concretes. The purpose of this study is to recommend to optimum mix proportions of antiwashout underwater concretes according to compressive strength of 300kgf/<TEX>$\textrm{cm}^2$</TEX> to 500kgf/<TEX>$\textrm{cm}^2$</TEX>. The antiwashout underwater concretes are prepared with various unit cement content, unit water content, sand-aggregate ratio, unit antiwashout agent and superplasticizer content. And they are tested for flowability, and compressive strength. From the test results, it is possible to recommend the optimum mix proportions of antiwashout underwater concretes according to compressive strengths within the range of 300kgf/<TEX>$\textrm{cm}^2$</TEX> to 500kgf/<TEX>$\textrm{cm}^2$</TEX>.

A Fundamental Study on Concrete Substituted Cement with Industrial By-Products

In this research, we have carried out the fundamental research on development of high strength concrete using the powder combining three industrial by-products as substitute of cement. The by-products used were fly ash of type II, ground granulated blast-furnace slag and gypsum. As a result,-it was possible to make a high strength paste, using vibrating compaction, with a water-powder ratio of 25%, The paste had compressive strength greater than 60 N/mm2 after curing for 91 days. Further we found it was possible to make high strength concrete of varying sand-aggregate ratios which all had a compressive strength of about 30 N/mm2 after curing for 28 days and 40 N/mm2 after curing for 91 days. Finally we obtained the optimum mixture proportion of concrete is unit water content = 170 kg/m3, water-powder ratio = 25%, and sand-aggregate ratio = 40%, For each of these results no cement was used.

フライアッシュを使用した高流動コンクリートの調合要因が流動特性に及ぼす効果

This paper is intended to study the effects of the mix proportion on the theological figures of the high-fluidity concrete using fly ash. The relationship between the mix proportion and the fluidity of the concrete was investigated regarding several experimental factors such as the kind of fly ash, the mixing ratio of fly ash to the normal cement, the mixing ratio of super plasticizer and viscosity agent, and sand aggregate ratio, etc. The rheological characteristics of the high-fluidity concrete such as plastic viscosity and yield value were measured by using the J shaped flow test. The main results are as follows. 1) In case of increasing the mixing ratio of Type I fly ash and Type II fly ash, the plastic viscosity and the yield value decrease. In case of increasing the mixing ratio of Type IV fly ash, these values increase. 2) The plastic viscosity of the concrete using Type I fly ash is smaller than that of the concrete using Type II fly ash. 3) The yield value of the concrete using Type I fly ash is nearly the same as that of the concrete using Type II fly ash.

Calculation of sand–aggregate ratio and water dosage of ordinary concrete

In the calculation of concrete mix proportion, sand–aggregate ratio and water dosage are determined by referring table, which is fairly arbitrary. In this paper, according to the concept of coordination number and Bingham model rheology, we deduced the formulas of sand–aggregate ratio and water dosage, respectively, and then utilized the experimental data to test and verify the formulas. Thereby, the calculation of sand–aggregate ratio and water dosage is more exact.

コンクリートの曲げ強度および収縮率に及ぼす養生方法と調合要因の効果に関する研究

This paper is intended to study the relationship between the flexural strength or the shrinkage ratio and the curing method or the mixing proportions of the concrete, were influenced such as the admixture, kinds of the cements and the aggregates. As the results, it was found that the concrete have the high flexural strength and the small shrinkage ratio when they were mixed with the silica fume and cured in 60℃ hot water about 6 days. And especially, it was found that the concrete have very high flexural strength and low shrinkage ratio when the cement included more than 0.35% of Na_2O, when the sand-aggregate ratio was more than 60% or when the sand-cement ratio was about 1.6.

粒形判定実積率を考慮した砕砂コンクリートの調合設計方法の研究

The particle shape of crushed fine aggegates is determined by the type of rock and the crushing equipment used. Any adequate index which indicate the particle shape of fine aggregates has not been found up to now. Therefore, in this country, reduced natural fine aggregates brings wide use of crushed fine aggregate while without the index of particle shape. Here, author have advanced a new method for indicate the particle shape of fine aggregate by solid content ratio measured with shieved particle which all path 2.5mm shieve and retain on 1.2mm shidve. (Here after, this ratio is called as solid content ratio for shape indicator and shortened into M_V). The numerical values of M_V are spreaded from 53% (crushed sand rock) to 65% (fine river sand), but it appears that the M_V is a good indicator of the amount of water used in a unit volume of concrete mix. A relation showing the quantity of water, in case of water cement ratio is 60% and sand aggregate ratio is 43%, for different M_V is given in Fig.1, for both non-airentrained and airentrained concrete, also it is formularized into formula (4). Minimum requirment of fine aggregates without segregation for defferent M_V is given in Fig.(3), and the equation for estimating S/A from M_V is shown as formula (8). Relations between compressive strength and M_V is shown in Fig.(8). The deta generally indicate that the compressive strength is increased by decreasing M_V. However, the elasticity of concrete is decreased by decreasing M_V.