Design Compressive Strength Research Articles

Carbon reduction of precast concrete under the marine environment

In this study, precast concrete panel was developed by substituting blast-furnace slag for part of the unit weight of cement in the precast concrete mix. A life cycle assessment technique was used to estimate the carbon dioxide reduction. Carbon reduction in the materials as well as during the production phase was considered. Blast-furnace slag substitution ratios of 50, 60, and 70wt.% were used to develop the precast concrete panel formulation. The steam curing time was taken as a variable with values of 8, 7, 6, 5, and 4h. Results showed that the precast concrete panel formulation with 60% of the unit weight of cement replaced by blast-furnace slag satisfied the design compressive strength criterion when steam curing was applied for 6h. The carbon dioxide emission was 33.8% lower than that of the control mix, which underwent no blast-furnace slag substitution and 8h of steam curing.

Investigating Approaches for Three-Dimensional Printing of Hydroxyapatite Scaffolds for Bone Regeneration

This study investigated the feasibility of manufacturing hydroxyapatite (HA)-based scaffolds using 3D printing technology by incorporating different binding additives, such as maltodextrin and polyvinyl alcohol (PVOH), into the powder formulation. Different grades of PVOH were evaluated in terms of their impact on the printing quality. Results showed that scaffolds with high architectural accuracy in terms of the design and excellent green compressive strength were obtained when the PVOH (high viscosity) was used as the binding additive for HA.

80 MPa급 고강도 콘크리트를 활용한 2거더교 RC 장지간 바닥판의 최소두께

To ensure durability and light weight of bridges, high-strength concrete is required for long-span deck slabs. Such a technology eventually extends the life of bridges and improves the economic efficiency. The results of this study suggests a formula for calculating the minimum thickness of long-span deck slabs built with high strength concrete. The minimum thickness is proposed based on the limit states indicated in the CEB-FIP Model Code and the Korean Highway Bridge Design Code(limit state design). The design compressive strength of concrete used for the study is 80MPa. Moreover, the required thickness for satisfying the flexural capacity and limiting deflection is estimated considering the limit state load combination. The formula for minimum thickness of deck slabs is proposed considering the ultimate limit state(ULS) and the serviceability limit state(SLS) of bridges, and by comparing the Korean Highway Bridge Design Code and similar previous studies. According to the research finding, the minimum thickness of long-span deck slab is more influenced by deflection limit than flexural capacity.

Flexural tests on pre-tensioned lightweight concrete beams

Eight pre-tensioned beams made using lightweight concrete with a design compressive strength of 35 MPa were tested under two symmetrical third-point concentrated loads. The main variables investigated were the eccentricity and effective prestress of the strands and the partial prestressing ratio. The flexural capacity of the beam specimens was compared with predictions obtained from simple equations using the equivalent stress block combined with different formulas proposed for the stress of bonded tendons at the ultimate strength of beams and from non-linear strain compatibility analysis. Test results showed that the normalised flexural capacity measured from pre-tensioned lightweight concrete beams with a reinforcing index below 0·15 was comparable to that of pre-tensioned normal-weight concrete beams with a similar reinforcing index, while that of a pre-tensioned lightweight concrete beam with a reinforcing index of 0·207 was lower than that of pre-tensioned normal weight concrete beams with a reinforcing index of 0·2. As a result, the increasing rate of normalised flexural capacity against the reinforcing index in pre-tensioned lightweight concrete beams was slightly lower than that observed in pre-tensioned normal weight concrete beams. The flexural capacity of pre-tensioned concrete beams predicted using an equivalent stress block was marginally influenced by the values determined from different formulas for the stress of bonded tendons at the ultimate strength of beams, although the ratio of the measured and predicted flexural capacities was commonly lower in pre-tensioned lightweight concrete beams than in pre-tensioned normal weight concrete beams.

The Evaluation of the Axial Strength of Composite Column with HSA800 Grade Steel

건축구조기준에 따라 HSA800 강재의 합성기둥 적용시에는 실험 또는 해석적 방법을 통하여 적용의 타당성을 검증해야 한다. 이에 본 연구에서는 합성기둥으로 주로 사용되는 H형강 매입형, 각형강관 및 원형강관 충전형 합성기둥 단면을 대상으로 HSA800 강재를 적용한 단주압축실험을 실시하고, 이를 통하여 축방향 내력 및 건축구조기준의 합성기둥 설계압축강도 설계식 적용의 타당성을 평가하였다. 실험결과 매입형 합성기둥의 경우 HSA800 강재의 설계기준항복강도를 저감없이 사용하기 위해서는 건축구조기준의 설계압축강도 산정식의 조정이 필요한 것으로 나타났으며, 이를 위해 띠철근 간격 조정 및 콘크리트의 유효단면적 사용을 제안하였다. 충전형 합성기둥의 경우에는 각형, 원형충전강관 기둥 모두 별도의 강도 저감이나 설계압축강도 산정식의 조정 없이 사용이 가능할 것으로 판단된다. According to the Korean Building Code (KBC), the validity of the application of 800MPa grade steel(HSA800) to composite column should be verified by experimental or analytical method. Thus, stub column tests for encased and filled composite members with HSA800 steel were conducted, and axial strength and the validity of design compressive strength equations in KBC were evaluated. The test results show that the equation of the compressive strength of encased composite column member in KBC should be modified in order to use HSA800 steel without any reduction of specified minimum yield strength. For this purpose, it is suggested that the interval of hoop should be narrowed and the effective concrete area should be used. The equation of the compressive strength of filled composite column member in KBC is applicable to filled composite column with HSA800 steel without any modification.

Fresh and Hardened Properties of Concrete Incorporating Recycled Glass as 100% Sand Replacement

AbstractThis paper investigates the use of glass cullet as a 100% sand replacement in Portland cement concrete (glasscrete) systems. Specifically, this paper evaluates the fresh and hardened properties of these systems in comparison with conventional natural sand concretes on the basis of similar 28-day design compressive strength, or the same w/cm. The results show that glasscrete mixtures need a lower w/cm to match the 28-day compressive strength of conventional concrete. In addition, glasscrete mixtures have greater elastic modulus, less drying shrinkage, less water sorptivity, and greater resistance against chloride ion penetration. Empirical curves are developed to provide material engineers and suppliers with necessary design specifications on the proper w/cm to implement when proportioning glasscrete mixtures. This study concludes that glasscrete mixtures are producible with adequate consistency and mechanical and durability performance, as long as the alkali-silicate reaction is properly controlle...

An Estimation on the Performance of High Fluidity Anti-Washout Underwater Concrete

The placing of anti-washout underwater concrete for the increasing construction of offshore foundations of long-span bridges at relatively deep sea is accompanied with significant loss of the quality of concrete as well as of the durability and reliability of the structure due to limitations brought by the workability of the high-pressure pump and the performance of the anti-washout agent. Therefore, the improvement of the performance of the underwater anti-washout agent and the development of high fluidity anti-washout underwater concrete exhibiting improved packing ability and fluidity should be implemented. Accordingly, this study focuses on the concrete for foundations applied in the RCD (Reverse Circulation Drill) method. The adequate mix proportions of a high fluidity anti-washout underwater concrete satisfying a design compressive strength of 35 MPa, slump flow larger than 600 mm and with less than 50 mg/ℓ of suspended solids is derived and the corresponding characteristics are evaluated.

Combined effects of recycled aggregate and fly ash towards concrete sustainability

The recycling of demolished concrete has been emerging as a sustainable solution to warrant the reduction of construction wastes, as well as to prevent the depletion of natural resources from growing construction demand. Nevertheless, some key factors that would affect the properties of recycled aggregate concrete have not been thoroughly investigated, such as the proportion of recycled aggregates, the moisture state of recycled aggregates, and the design compressive strength of concrete. In particular, little research was done on the combined effects of recycled aggregates and fly ash, popularly used as a partial substitution of cement. Given the concerns, this study investigates the effects of such factors on the mechanical and durability properties of recycled aggregate concrete. Eleven cases of concrete mixtures were tested for the rheological properties of fresh concrete, compressive strength, tensile strength, and chloride diffusion coefficient. In general, the higher ratio of recycled aggregates resulted in the better flowability of concrete. Also, the use of fly ash improved the flowability of recycled aggregate concrete. The strength test results showed that the higher ratio of recycled aggregates generally caused the lower compressive and tensile strengths of concrete. However, the cases with 30% recycled aggregates showed only slight compressive strength reductions. Similarly, the use of fly ash caused only small reductions in the compressive strength of recycled aggregate concrete. In contrast, the negative effects of recycled aggregates and fly ash were greater in the tensile strength than in the compressive strength. Lastly, the cases containing fly ash exhibited much higher resistance to chloride penetration, even in the cases with recycled aggregates.

Flexural Performance of Laterized Concrete made with Blended Flyash Cement (Fa-Latcon)

This paper presents the results of the experimental assessment of the Flexural performance of Fly ash Laterized concrete (FA-LATCON). Test were conducted on concrete mixtures which was obtained by replacing 0 and 20% by weight of ordinary portland cement (OPC) with Fly ash (FA) and replacement of fine aggregate (sand) with Laterite (Lat.) by 0%, 10%, 20% and 30% for hydration period of 7, 21, 28 and 56days. Series of tests on fresh and hardened properties on FA-LATCON was carried out. The design mix was made for 28days target strengths of 25N/mm 2 with 0.65 water to Binder ratio. The Flexural strength measured after 28days of curing increase with age but decrease with increase in Laterite and FA content respectively. The FA-LATCON Flexural strength performance was satisfactory having achieved a least ratio of 28days Flexural strength to 28-days design compressive strength of 0.273.

폴리믹스 혼입 고강도 콘크리트의 펌프압송 성상에 관한 실험적 연구

기존 내화성능 확보기술인 섬유혼입 콘크리트의 경우 내화성능을 높이기 위해 섬유량이 과다하게 투입되면 초고압 펌핑시 엉킴현상이 발생하여 압송효율이 급격히 저하되는 문제점이 있다. 이에 이 연구에서는 기존 섬유 이외에 추가로 유동성 개선효과 및 내화성능을 확보할 수 있는 폭렬방지재를 개발하여 이를 활용한 60~80 MPa 고강도 콘크리트의 펌프압송성능 개선을 이 연구의 목표로 설정하였다. 이 연구에서 사용된 폭렬방지재는 pp섬유, 나일론 섬유 및 폴리머 분말을 혼입한 폴리믹스로서 이를 활용한 결과는 다음과 같다. 섬유혼입 유무에 따른 굳지않은 특성 중 슬럼프 플로우는 섬유투입시 압송 후 기존 대비 약 70% 물성이 개선되었고, 공기량은 섬유혼입에 관계없이 압송 후 다소증가하였다. 압축강도는 재령 28일에서 설계기준강도를 상회하였고, 휨 강도는 압축강도 발현율 대비 12~15%로 기존 경향과 유사하게 나타났다. 탄성계수는 섬유혼입시 감소하였지만, 기준값 이상으로 문제는 없을 것으로 사료된다.

DEVELOPMENT OF AN OPTIMUM PRE-FOUNDED COLUMN SYSTEM FOR TOP-DOWN CONSTRUCTION

In this work, circular concrete-filled steel tubular (CCFT) columns, rather than the more popular H-shaped columns, were suggested as pre-founded columns for top-down construction. In addition, a novel shear connection system with headed stud shear connectors between the CCFT columns and the flat slabs was developed. It was noted that a CCFT column with a design compressive strength similar to that of an H-shaped column without consideration of length effects can be easily installed, even into a smaller borehole. Furthermore, compared to the H-shaped column, less steel is required for the CCFT column. It was shown that the amount of steel needed can be reduced by decreasing the wall thicknesses or diameters of the CCFT column depending on the exposed length of the column during excavation. The fillet-welded joint of the developed shear connector system was also tested before its in-situ application. The test results revealed that the joint possessed sufficient shear and deformation capacities. The CCFT column with the developed shear connection system was ultimately applied to an actual top-down construction process. The good constructability of the CCFT column system and reductions in construction costs and time were confirmed.

Dynamic Characteristics Evaluation of Innovative UHPC Pedestrian Cable Stayed Bridge

KICT (Korea Institute of Construction Technology) is conducting a project called “SUPER BRIDGE 200—Development of Low Cost and Long Life Hybrid Cable Stayed Bridge”. This project aims to reduce the construction and main- tenance costs of long-span bridges by 20% and double their lifetime through the exploitation of ultra-high performance concrete (UHPC). This paper presents the design and construction of the first pedestrian cable stayed bridge using UHPC developed by KICT. UHPC, compared to conventional concrete, has not only high compressive and tensile strengths but also high ductility. The UHPC developed at KICT is a steel fiber-reinforced cement compound presenting design compressive strength larger than 180 MPa and design tensile strength exceeding 10 MPa with water-to-binder ratio below 0.24 and admixing of 2 volume percentage of steel fiber. To show the applicability of UHPC to structures, a pedestrian cable stayed bridge (Super Bridge I) exploiting the characteristics of the developed UHPC has been planned, designed and erected at KICT. The dimension of UHPC deck is 2.7 m × 7 m as a precast segment with a typical thickness of deck of only 7 cm. However, harmful crack was observed in the deck at the time of the fabrication of the deck segments. Accordingly, new fabrication method was conceived and applied to prevent cracking of the UHPC slender deck. Four UHPC deck segments were fabricated successfully without any crack. After construction, the dynamic characteristics (natural frequencies and mode shapes) were evaluated through vibration tests since several users felt excess vibration. A vertical tuned mass damper (TMD) was proposed and installed on the parapet of the bridge. The TMD reduces the acceleration by about 30% from 0.0316 g to 0.0244 g when two pedestrians are crossing the bridge.

Optimised Mix Design for Normal Strength and High Performance Concrete Using Particle Packing Method

Abstract This paper presents the details of optimized mix design for normal strength and high performance concrete using particle packing method. A critical review of mix design methods have been carried out for normal strength concrete using American Concrete Institute (ACI) and Bureau of Indian Standards (BIS) methods highlighting the similarities and differences towards attaining a particular design compressive strength. Mix design for M30 and M40 grades of concrete have been carried out using ACI, BIS and particle packing methods. Optimization of concrete mix has been carried out by means of particle packing method using EMMA software, which employs modified Anderson curve to adjust the main proportions. Compressive strength is evaluated for the adjusted proportions and it is observed that the mixes designed by particle packing method estimates compressive strength closer to design compressive strength. Further, particle packing method has been employed to optimize the ingredients of high performance concrete and experiments have been carried out to check the design adequacy of the desired concrete compressive strength.

비부착 프리스트레스트 경량 콘크리트 보의 휨 거동에 대한 부착 철근과 유효 프리스트레스의 영향

포스트텐션 경량 콘크리트(LWC) 보 시험체 7개가 상부 대칭 2점 집중 하중 하에서 실험되었다. 주요 변수는 부착 주철근 양 및 유효 프리스트레스 양이다. 경량 콘크리트의 설계강도 및 단위 용적 중량은 각각 30 MPa과 1,770 kg/㎥ 이다. 포스트텐션 보통 중량 콘크리트에서와 같이 균열 진전과 비부착 긴장재의 응력은 부착 철근 및 유효 프리스트레스 양에 의해 영향을 받았다. 부착 철근 및 유효 프리스트레스 양의 증가와 함께 보의 사용성과 휨 내력은 향상되는 반면 비부착 긴장재의 응력은 감소하였다. 포스트텐션 경량 콘크리트 보의 균열 제어를 위해서는 ACI 318-08에서 제시하는 최소 부착 철근이 요구되었다. 포스트텐션 경량 콘크리트 보의 휨 거동 및 비부착 긴장재의 응력 증가는 제시된 비선형 해석 모델에 의해 적절하게 예측될 수 있었다. 반면 ACI 318-08 기준은 포스트텐션 LWC 보의 휨 내력 및 비부착 긴장재의 응력 증가에 대해 지나치게 안전측에 있었다.

건조수축에 따른 균열 방지를 위한 콘크리트 슬래브의 정량적 줄눈 간격 산정

콘크리트 슬래브의 수축으로 인해 발생하는 응력에 의한 무분별한 균열을 억제하기 위해 줄눈을 설치한다. 그러나 설치된 줄눈의 간격은 구체적인 산출 근거나 정량적인 기준 없이 경험적으로 나누어지고 있다. 따라서 이 연구에서는 콘크리트 슬래브의 수축 응력에 의한 변형량을 측정하고 이에 따른 정량적인 평가 기준을 제시하고자 한다. 노출된 환경 조건은 온도 15oC, 상대습도 60%를 적용하였다. 건조수축 실험은 현재 슬래브 설계에 많이 사용되는 설계강도 30 MPa 및 40 MPa 배합을 사용하였고 그 결과를 기존 건조수축 모델에 적용하였다. 그 결과 ACI 209R 모델에 가장 일치하는 것으로 나타났으며 이를 바탕으로 콘크리트 슬래브의 정량적인 줄눈 간격을 산정하였다.

Comparison of in situ properties of wall elements cast using self-consolidating concrete

An experimental program was undertaken to investigate the homogeneity of in situ properties of wall elements cast with various commercially available self-consolidating concrete (SCC) mixtures. Wall elements measuring 5 m in length, 1.6 m in height, and 0.35 m in width were cast. The SCC mixtures were proportioned with various binders and admixtures and had different levels of slump flow consistency and design compressive strengths. The SCC mixtures exhibited adequate passing ability with L-box blocking ratio higher than 0.70 and filling capacity greater than 80%. All cast walls exhibited homogeneous in situ mechanical properties, regardless of the core location. The coefficient of variation (COV) of in situ compressive strength values ranged from 3 to 6%. Conventional vibrated concrete used to cast a reference wall element led to relatively large spread in in situ rapid chloride-ion permeability values and high COV of spacing factor compared to those of the various SCC wall elements (17% vs. 6–12%). Good correlation was established between surface settlement and top-bar factor of reinforcing bars embedded along the various heights of the 1.6-m high walls. On average, concrete with 0.50% surface settlement was shown to exhibit a maximum top-bar factor of 1.4. The mean top-bar factor values near the top of walls cast with SCC were limited to 1.4, which is considered a low value given the high slump flow of the concrete and the depth of cast elements.

Using Twist-Off Method for Measuring Surface Strength of Concretes Cured under Different Environments

This paper presents the results of a research project whose goal was to measure the surface strength of concretes cured under different environments by using the newly developed twist-off test. A circular steel disk was glued to the surface of the concrete with an epoxy resin. The force required to twist this disk off the surface, together with an attached layer of concrete, was measured by using an ordinary torque wrench. The different curing regimes had specimens immersed in drinking water, covered with a wet hessian and polythene sheet, kept in a dry laboratory, left in open air, steam cured, and coated with a curing agent. Eight different concrete mixtures with a 28-day design compressive strength of 10–75 MPa were used. The effects of different water-cement and aggregate-cement ratios were studied for all mixes cured under the six different environments. The coefficients of variation associated with surface-strength measurement were also studied for different curing regimes.

Experimental study and design calculation for compressive strengths of cold formed thick‐wall sections

In order to investigate section capacities of thick‐wall cold formed steel with square and rectangular hollow cross‐sections, experiments were carried out on mechanical properties of the flat coupons, corner coupons, parent steel coupons and full section stub columns. Strain hardening of cold forming thick‐wall cold formed sections was investigated. The stub column test strengths were compared with the design compressive strengths specified by the Australian/New Zealand and Chinese standards for the design of the cold formed steel structural members respectively. It has been shown that the strength predicted by the Australian/New Zealand standard using material properties and that forecasted by the Chinese standard based on the average design yield stress of the full section are a little conservative. The two mean strengths predicted by Australian/New Zealand standard based on the mean design yield stress and forecasted by the Chinese standard using material properties tests are identical, which are superior to the present thick‐wall cold formed steel tubes because of their safety and economy.

Effect of size and shape of specimen on compressive strength of glass fiber reinforced concrete (GFRC)

Concrete is a versatile material with tremendous applications in civil engineering construction. Structural concrete elements are generally made with concrete having a compressive strength of 20 to 35 MPa. Lately, there is an increase in use of high strength concrete (HSC) in major construction projects such as high-rise buildings, and bridges involving members of different sizes and shapes. The compressive strength of concrete is used as the most basic and important material property in the design of reinforced concrete structures. It has become a problem to use this value as the control specimen sizes and shapes are different from country to country. In India, the characteristic compressive strength is usually measured based on 150 mm cubes [1]. But, the ACI code of practice specifies the design compressive strength based on the standard 150x300 mm cylinders [2]. The use of 100x200 mm cylinders gained more acceptance as the need to test high strength concrete increases [3]. In this context the size and shape of concrete becomes an important parameter for the compressive strength. In view of the significance of compressive strength of concrete and due to the fact that the structural elements of different sizes and shapes are used, it is proposed to investigate the effect of size and shape of the specimen on the compressive strength of concrete. In this work, specimens of plain as well as Glass Fiber Reinforced Concrete (GFRC) specimens are cast in order to carry out a comparative study.

Structural Behavior of Story-High Cement-Stabilized Rammed-Earth Walls under Compression

A rammed-earth wall is a monolithic construction made by compacting processed soil in progressive layers in a rigid formwork. There is a growing interest in using this low-embodied-carbon building material in buildings. The paper investigates the strength and structural behavior of story-high cement-stabilized rammed-earth (CSRE) walls, reviews literature on the strength of CSRE, and discusses results of the compressive strength of CSRE prisms, wallettes, and story-high walls. The strength of the story-high wall was compared with the strength of wallettes and prisms. There is a nearly 30% reduction in strength as the height-to-thickness ratio increases from about 5 to 20. The ultimate compressive strength of CSRE walls predicted using the tangent modulus theory is in close agreement with the experimental values. The shear failures noticed in the story-high walls resemble the shear failures of short-height prism and wallette specimens. The paper ends with a discussion of structural design and characteristic compressive strength of CSRE walls.