Search

Many critical concreting activities require the determination of the in-place concrete strength. It can be costly to wait too long to execute these activities, but acting too early can have a negative impact on structural performance. Conventional moulded concrete cylinders and alternative strength assessment methods such as the maturity method are commonly used to assess concrete's in-place strength. This study is focused on a special case when the maturity method is applied for evaluating concrete strength in cold weather at an early age. Specifically, the study proposes an alternative method for calibrating the activation energy, an input for the maturity method. Concretes cured at two different temperatures are used to calibrate the activation energy. The maturity method based on this activation energy predicted the cold weather concrete's compressive strength satisfactorily. It was also found that for a successful application of the proposed activation energy calibration, the two temperatures should represent the expected minimum and maximum temperature at the site. Furthermore, the results showed that the maturity method based on the proposed activation energy calibration method performed better than the conventional cylinder method. [ABSTRACT FROM AUTHOR]

The paper investigates the freeze–thaw resistance and sorptivity behavior of fine‐grained alkali‐activated concrete cured at ambient temperature. A blended binder system containing fly ash, ground granulated blast furnace slag, and silica fume was used. A combination of sodium hydroxide and sodium silicate was used as an activator. The freeze–thaw resistance was evaluated based on mass loss (scaling), and the extent of internal damage was assessed by testing the ultrasonic time at different cycles. Initial and secondary sorptivity coefficients were calculated based on the cumulative water absorption values at different time intervals. Alkali content, sodium silicate to sodium hydroxide ratio, and water to binder ratio were investigated. The experimental results showed that water to binder ratio is the most significant parameter for the scaling; higher ratios result in higher scaling. In terms of internal damage, alkali content is the most significant. The increase of alkali increased the amount of internal damage in the concrete. The initial sorptivity coefficient increased with the water and alkali content and decreased with the silicate content. The secondary sorptivity coefficient showed no significant change with the investigated parameters. [ABSTRACT FROM AUTHOR]

Alkali-activated slag concrete (ASC) is regarded as one of the most promising sustainable construction materials for replacing ordinary Portland cement concrete (OPC) due to its comparable strength and outstanding durability in challenging environments. In this study, the corrosion of steel bars embedded in ASC and OPC was studied by means of an electrically accelerated corrosion test of steel bars in concrete. Meanwhile, the bond performance of the corroded steel bars embedded in ASC was tested and compared with corresponding OPC groups. The results showed that ASC and OPC behaved differently in terms of bond deterioration. The high chemical resistance of ASC decreased the corrosion of steel bars and, thus, increased the residue bond strength and the bond stiffness. [ABSTRACT FROM AUTHOR]

Combining different fiber types may improve the mechanical properties of fiber reinforced concrete. The present study is focused on investigating hybrid fiber reinforced concrete (HFRC) with steel and basalt fiber. Mechanical properties of fiber reinforced fine-grained concrete are investigated. The results demonstrate that using optimal steel and basalt fiber reinforcement ratios avoids concrete mixtures' segregation and improves their homogeneity. Concrete with hybrid steel and basalt fiber reinforcement has higher strength. Effective methodology for proper design of HFRC compositions was proposed. It is based on the mathematical experiments planning method. The proposed method enables optimal mix proportioning of high-strength fine-grained concrete with hybrid steel and basalt fiber reinforcement. [ABSTRACT FROM AUTHOR]

Bond behaviour plays an important role in the design and performance of reinforced-concrete structures. In this study, finite-element modelling is used to perform a parametric study. The bond between the glass fibre-reinforced polymer (GFRP) bar and alkali-activated cement concrete is modelled by surface-based cohesive behaviour. The accuracy of the model is validated by comparing model predictions with experimental results. The effect of concrete cover, bar diameter, compressive strength, lead length, embedment length and GFRP elastic modulus on bond behaviour is investigated. Each of these parameters are varied based on a range of applicable values to study their influence on bond behaviour. The parametric study showed that bond behaviour is mainly affected by concrete cover, bar diameter, embedment length and the compressive strength of the concrete. The effect of the elastic modulus of the GFRP bar is not as pronounced as that of the other parameters, while the influence of lead length can be avoided by providing enough unbonded length at the loaded end. The parametric study is further used to calibrate a well-known bond equation and develop a new regression equation for predicting the maximum bond stress. The predicted results from these equations showed a good agreement with the experimental results as well as those of the finite-element model. [ABSTRACT FROM AUTHOR]

• Compaction improves splitting resistance of vertically cast specimens. • Top-cast specimens have a lower splitting resistance than bottom-cast specimens. • Higher splitting stress is generated orthogonal to the plane of the textile. • The main cause of splitting failure is the fiber strand's varying cross-section. • Bond distribution depends on the cross-section variation along the fiber strand. Textile-reinforced concrete is an innovative combination of high-performance fine-grained concrete and textile reinforcements. This combination allows the production of thin, efficient, and durable structural elements. Impregnation is commonly used to improve the textile's mechanical performance. When stiff impregnation materials are used, a fiber strand with high transverse stiffness is formed. Textile-reinforced concrete structures with such fiber strands are prone to splitting failures. This paper investigates splitting failure in textile reinforced concrete experimentally and numerically. In the experimental part, the effect of concrete compaction, casting method, and position are studied as parameters. Finite element analysis is performed to investigate failure mode, tensile and bond stress distributions, and the effect of the varying cross-section of the fiber strand. Compaction improved the splitting resistance for the vertically cast specimens. The compacted vertically cast specimens showed a higher splitting resistance than their horizontally cast equivalents. The finite element model indicated that the main cause of splitting failure is the textile reinforcement's varying cross-section coupled with its flat elliptical shape. The model also showed that the bond stress distribution depends on the fiber strand's geometric configuration. [ABSTRACT FROM AUTHOR]

Concrete is the most commonly used construction material because of its various advantages, such as versatility, familiarity, strength, and durability, and it will continue to be in demand far into the future. However, with today's sensitivity to environmental protection, this material faces unprecedented challenges because of its high greenhouse gas emissions, mainly during cement production. This paper investigates one of the promising cement replacement materials, alkali-activated cement (AAC) concrete. Being produced mainly from byproduct materials and having a comparable structural performance to conventional concrete, AAC concrete can transform the construction industry. Mechanical properties such as compressive and flexural strength and the relationship between them are studied. Different source materials such as fly ash (FA), ground granulated blast furnace slag (GGBS), silica fume (SF), and Metakaolin (MK) are used. The effect of the source materials and the activator solutions on the concrete performance is studied. Furthermore, the freeze-thaw resistance of the concrete is studied. The study results showed that the behavior of AAC depends highly on the source material combinations and type used. The effect of the alkaline solution is also dependent on the source material used. Mixes with higher GGBS content showed the highest strength, while mixes with MK showed the highest flexural strength. The freeze-thaw test results showed that proper design of AAC concrete with lower water content is critical to achieving a good resistance. [ABSTRACT FROM AUTHOR]

The bond performance of fiber reinforced plastic (FRP) bars in seawater sea sand alkali activated concrete (SSASC) was investigated using pull-out test specimens. The effect of different concrete strengths, anchorage lengths, FRP bar types, and diameters on the bond performance were investiaged. Special emphasis was given to the applicability of the existing bond-slip constitutive models to FRP reinforced SSASC, which was investigated by calibrating well-known models to the experimental results. The correlation between the experimental curve and different bond-slip constitutive models is analyzed by calculating the R2 value. To verify the applicability of finite element analysis to SSASC and FRP bars system, numerical simulation was performed in ABAQUS finite element simulation software by setting the same conditions as the experimental variables. The results indicate that the Fan Xiaochun's model, which is the modifications of the MBPE model, has a high degree of correlation and is more suitable for SSASC and FRP bars system. The simulation results using ABAQUS finite element software are in good agreement with the experimental results. • We investigated the bond between FRP bars and alkali activated concrete (AAC). • We suggested bond-slip models for FRP-AAC. • AAC offers a potential solution for the effective use of FRP reinforcement. • The finite element model can be used for predicting bond behaviour of FRP-AAC. [ABSTRACT FROM AUTHOR]