Effects of Mix Proportions and Polypropylene Fibers Reinforcement on the Mechanical and Long-Term Durability Behavior of Carbonated Concrete

Effect of mix proportion and reinforcement size on the anchorage bond stress of laterized concrete

Lithium slag (LS), a solid waste generated during lithium smelting, exhibits significant potential for geopolymer preparation. However, the high shrinkage of lithium slag geopolymer mortar (LSGM) severely restricts its engineering application. Currently, research on the effects of mix proportions (GBFS-LS mass ratio, water–binder ratio, and binder–sand ratio) on LSGM’s shrinkage, and the correlation between shrinkage behavior and microstructures (pore structure and thermal behavior), remains insufficient. Additionally, there is a lack of targeted shrinkage prediction models for LSGM. To address these research gaps, this study systematically investigates the shrinkage characteristics of LSGM and develops a modified prediction model. Thermogravimetric analysis–differential thermal gravimetric analysis (TG-DTG) results show that a lower GBFS-LS ratio promotes the formation of dense sodium-alumino-silicate hydrate (N-A-S-H) gels. Meanwhile, mercury intrusion porosimetry (MIP) tests demonstrate that optimizing the water–binder ratio and binder–sand ratio refines the pore structure of LSGM, where the average pore size is reduced from 53.5 nm at a GBFS-LS ratio of 3 to 28.75 nm at a GBFS-LS ratio of 1.5.Quantitatively; compared with the group with a GBFS-LS ratio of 3, the 90-day shrinkage strain of the group with a GBFS-LS ratio of 1.5 decreases by 25.8%. When the water–binder ratio decreases from 0.57 to 0.27, the 90-day shrinkage strain reduces by 36.7%; in contrast, increasing the binder–sand ratio from 0.21 to 0.39 leads to a 39.8% increase in 90-day shrinkage strain. Based on the experimental data and the fundamental framework of the American Concrete Institute (ACI) model, this study introduces mix proportion influence coefficients and constructs a novel shrinkage prediction model tailored to LSGM. The coefficient of determination (R2) of the proposed model exceeds 0.98. This model provides a reliable quantitative tool for the mix proportion optimization and engineering application of LSGM.

Effect of mix proportions on plastic shrinkage cracking of concrete in hot environments

In pursuits of sustainable infrastructure, development of Low Carbon Concrete (LCC) is vital for the construction of Low Carbon Structures (LCS). For LCS to be widely applied, it is imperative that LCC exhibits the required mechanical and durability characteristics. This necessitates an understanding of constituents such as supplementary cementitious materials (SCMs), recycled aggregates (RA) and fibres that influence LCC mechanical and durability behaviours. However, based on materials characterisation, previous studies reveal significant variations in LCC mechanical properties and durability behaviours. Therefore, this review seeks to comprehend the effect of different types of SCMs, RA and fibres on key mechanical properties and durability behaviours of LCC. It also provides insights on improving LCC mechanical properties and durability behaviours, drawing from extensive research outlooks on materials characterisations, mix proportioning and curing conditions and summarises existing literature on LCC carbon footprint analysis. Finally, it identifies potential research directions for future studies including analytical models to enhance the mechanical properties and durability behaviours of LCC. • A comprehensive literature review on low carbon concrete (LCC) is presented. • The review covers both mechanical properties and durability performance of LCC. • Review on carbon footprint analysis of LCC also included. • Gaps of knowledge and potential future research directions are identified.

Effects of mix proportion and curing condition on shrinkage behavior of HPFRCCs with silica fume and blast furnace slag

To examine how far the effect of mix proportion in fresh concrete and in hardened concrete, centrifugally placed, upon its properties is dependent on its conditions, six sorts of sand graded according to grain size were selected and several rates of mix proportion s/a were determined for the experiments, which have been performed with these selected materials thus variously mixed. The tests of fresh concrete have been performed to investigate the mutual relation between the different grade of sand and different rate of mix proportion s/a on one hand and on the other the water content required for maintaining constant consistency. Investigation has also been made of the efficacy of water-reducing admixture. The tests of hardened concrete have been made to find the effects of the above mentioned conditions in mixing proportion on the segregation and separation of centrifugally placed concrete, and to ascertain its manifest gain in strength. The main results obtained by them are as follows.(1) Of the fine aggregates of different grades in grain size of sand, the finer part has effects on the water content, while the coarser part on the mix proportion s/a respectively, and when the mix proportion is properly determined, the centrifugally placed concrete with gap grades of sand will occasionally make better concrete of higher strength with smaller segregation.(2) The use of water-reducing admixture of good quality will remarkably raise the workability of fresh concrete, and considerably reduce the segregation and separation of centrifugally placed concrete.

Summary Following recent studies of concrete as a composite material, this paper examines whether there is a relation between the mix proportions and properties of the constituents and the over-all Poisson's ratio for mortars and concretes. From an examination of available and new data, it is apparent that Poisson's ratio is affected by the method of testing, the mix proportions, and the moisture condition and temperature of the specimens. Approximate expressions are proposed for the static and dynamic Poisson's ratios of saturated mortars and concretes made with gravel aggregates in terms of the volume fractions and Poisson's ratios of the constituent aggregate and cement paste phases. Static and dynamic tests do not measure the same properties of concrete, and suggestions are made for the differences between them.

A study to achieve high-strength, high porosity and permeability pervious concrete pavement was carried out. Mix proportions in terms of cement content, coarse aggregate-cement ratio (CA/C) and water-cement (W/C) ratio were varied. A mix proportion providing the optimal combination of strength and porosity was chosen, and polymer superplasticizers were added to examine their effect on the strength and porosity. Results showed that a water-cement ratio of 0.2 resulted in a dry and brittle mix that led to compressive strength less than 15MPa but a high permeability rate of approximately 20mm/s. A mix with w/c ratio of 0.3 and CA/C ratio of 4.25 resulted in compressive strength of 13.9MPa, flexural strength of 3MPa and high porosity of more than 20%. The use of high cement content of 495kg/m3 in the mix resulted in high compressive strengths of 51.8MPa, flexural strength of more than 4MPa, however permeability was reduced to approximately 1mm/s.

Summary The compressive strength of concrete at a constant cement/water ratio is shown to decrease with increasing cement contents and therefore confirms earlier work in Europe. This decrease, however, is generally quite small especially for the uniaxial compressive strength. Two exceptions are possible, depending upon the sand content: at high sand contents a critical maximum sand/cement ratio is exceeded such that air voids become unavoidable and the strength decreases with decreasing cement content; at low sand contents a critical minimum sand/cement ratio is not attained and large losses in strength then occur with increasing cement contents. The critical minimum sand/cement ratio depends upon the type and grading of the aggregate and the mix proportions. It is due to the onset of very extensive ‘water gain’ and to the lack of adequate restraint to shrinkage of the cement paste. These effects can (and should) be avoided in normal concretes. The presence of dust in the fine aggregate can be beneficial.for low-strength concretes probably because of its ability to modify the structure o.fthe cement paste and reduce the water gain. It has little effect on high-strength concretes.

본 연구는 SP제 및 물시멘트비 영향에 따른 변화를 고려한 초유동 콘크리트의 유동 실험 및 해석 시뮬레이션 기법에 관해 소개한 것이다. 국내에서 생산되는 시멘트, 골재 및 SP 혼화제를 대상으로 하여 배합조건에 따른 유동 콘크리트의 레올로지 특성 및 유동현상 실험을 수행하였으며, 이로부터 물시멘트비와 SP제의 영향을 고려한 유동 콘크리트의 레올로지 정수 추정에 관한 예측모델을 제시하였다. 제시된 두 배합조건에 의한 영향을 유동 콘크리트의 전단응력과 변형률속도 관계 정식화에 적용하여 본 해석 모델을 제시하였다. SP제 및 물시멘트비의 변화를 고려한 초유동 콘크리트의 L형 박스 흐름 실험을 수행하여 해석 시뮬레이션 모델과 비교하여 개발 모델에 대해 평가토록 하였다.

This article experimentally and numerically investigated the flexural behavior of T‐shaped UHPFRC beams reinforced with high‐strength bars. A total of five beams were tested to study the effect of steel fiber volumetric ratio, longitudinal reinforcement ratio, and mix proportion of UHPFRC. Test results indicate that flexural stiffness and strength increased with increasing reinforcement ratio, while the effect of mix proportion was negligible. With the same shear reinforcement ratio, the failure mode of T‐shaped beams changed from shear failure to flexural failure with steel fibers. Results from finite element analyses had good agreement with test results. Future research will focus on the parametric study based on calibrated finite element models and the secondary development of ABAQUS to simulate the shear failure of UHPFRC beams.

本研究では、環境条件がコンクリート構造物の中性化の進行に及ぼす影響を評価するため、薄板状の小型モルタル供試体を2つの橋梁および浄水場施設の4構造物に貼り付けて暴露し、実構造物の異なる部位における環境条件の影響を評価した。また、モルタルの配合および暴露時期が中性化環境評価に及ぼす影響について検討した。その結果、雨掛かりの無い環境条件下では、薄板供試体によって中性化環境評価が可能であることが確認できた。また、短期間の暴露試験によって長期供用された構造物中性化深さを評価するには、中性化しやすい配合で供試体が乾燥しやすい時期の暴露が適していることが確認できた。

Effect of mix proportion, water-cement ratio, age and curing conditions on the dynamic modulus of elasticity of concrete

Modeling moisture transport at the surface layer of fatigue-damaged concrete

Discussion: The effect of mix proportions and method of testing on Poisson's ratio for mortars and concretes