Workability and Flexural Properties of Fibre-Reinforced Geopolymer Using Different Mono and Hybrid Fibres

The effects of mono (single type) and hybrid (mixed types) fibres on the workability, compressive strength, flexural strength, and toughness parameters of fly ash geopolymer mortar were studied. The ratio of sand to geopolymer paste of the mortar was 2.75. It was found that workability of mortar decreased more with the use of PP fibres due to its higher dispersion into individual filaments in geopolymer mortar compared to the bundled ARG and PVA fibres. Compressive strength increased by 14% for using 1% steel with 0.5% PP fibres compared to that of the control mixture, which was 48 MPa. However, 25 to 30% decrease of compressive strength was observed in the mortars using the low-modulus fibres. Generally, flexural strength followed the trend of compressive strength. Deflection hardening behaviours in terms of the ASTM C1609 toughness indices, namely I5, I10 and I20 were exhibited by the mortars using 1% steel mono fibres, 0.5% ARG with 0.5% steel and 1% PVA with 0.5% steel hybrid fibres. The toughness indices and residual strength factors of the mortars using the other mono or hybrid fibres at 1 or 1.5% dosage were relatively low. Therefore, multiple cracking and deflection hardening behaviours could be achieved in fly ash geopolymer mortars of high sand to binder ratio by using steel fibres in mono or hybrid forms with ARG and PVA fibres.

Probabilistic Finite Element Modeling of Textile Reinforced SHCC Subjected to Uniaxial Tension

The paper presents a finite element investigation of the effect of material composition and the constituents’ interaction on the tensile behavior of strain-hardening cement-based composites (SHCC) both with and without textile reinforcement. The input material parameters for the SHCC and continuous reinforcement models, as well for their bond, were adopted from reference experimental investigations. The textile reinforcement was discretized by truss elements in the loaded direction only, with the constitutive relationships simulating a carbon and a polymer textile, respectively. For realistic simulation of macroscopic tensile response and multiple cracking patterns in hybrid fiber-reinforced composites subjected to tension, a multi-scale and probabilistic approach was adopted. SHCC was simulated using the smeared crack model, and the input constitutive law reflected the single-crack opening behavior. The probabilistic definition and spatial fluctuation of matrix strength and tensile strength of the SHCC enabled realistic multiple cracking and fracture localization within the loaded model specimens. Two-dimensional (2D) simulations enabled a detailed material assessment with reasonable computational effort and showed adequate accuracy in predicting the experimental findings in terms of macroscopic stress–strain properties, extent of multiple cracking, and average crack width. Besides material optimization, the model is suitable for assessing the strengthening performance of hybrid fiber-reinforced composites on structural elements.

Fracture Energy, Fatigue and Creep Properties of Engineered Cementitious Composites Incorporating Fly Ash/Slag with Different Aggregates

This thesis investigates the influence of microsilica sand and local crushed sand, and different supplementary cementing materials on the mechanical properties of engineered cementitious composites (ECCs). ECC is a special type of high performance fiber reinforced cementitious composite with high ductility which exhibits strain-hardening and multiple-cracking behaviours in tension. The use of local aggregates in ECC production can lower its cost to mitigate the obstacles of wider commercial use. The experimental results showed that multiple-cracking behaviour was developed under fatigue loading for fly ash ECC (FA-ECC) mixtures, and the number of cracks was lower at both lower fatigue stress level and higher fatigue number of cycles. FA-ECC mixtures with silica sand exhibited higher deflection evolution under fatigue loading than FA-ECC mixtures with crushed sand. Based on the experimental results on link slab specimens, both FA-ECC mixtures with silica and crushed sands exhibited almost the same creep behaviour.

Fracture Energy, Fatigue and Creep Properties of Engineered Cementitious Composites Incorporating Fly Ash/Slag with Different Aggregates

This thesis investigates the influence of microsilica sand and local crushed sand, and different supplementary cementing materials on the mechanical properties of engineered cementitious composites (ECCs). ECC is a special type of high performance fiber reinforced cementitious composite with high ductility which exhibits strain-hardening and multiple-cracking behaviours in tension. The use of local aggregates in ECC production can lower its cost to mitigate the obstacles of wider commercial use. The experimental results showed that multiple-cracking behaviour was developed under fatigue loading for fly ash ECC (FA-ECC) mixtures, and the number of cracks was lower at both lower fatigue stress level and higher fatigue number of cycles. FA-ECC mixtures with silica sand exhibited higher deflection evolution under fatigue loading than FA-ECC mixtures with crushed sand. Based on the experimental results on link slab specimens, both FA-ECC mixtures with silica and crushed sands exhibited almost the same creep behaviour.

Mechanical Behavior of Ultrahigh-Performance Concrete Tunnel Lining Segments

Ultrahigh-performance concrete (UHPC) is a novel material demonstrating superior mechanical, durability and sustainability performance. However, its implementation in massive structures is hampered by its high initial cost and the lack of stakeholders’ confidence, especially in developing countries. Therefore, the present study explores, for the first time, a novel application of UHPC, incorporating hybrid steel fibers in precast tunnel lining segments. Reduced scale curved tunnel lining segments were cast using UHPC incorporating hybrid 8 mm and 16 mm steel fibers at dosages of 1%, 2% and 3% by mixture volume. Flexural and thrust load tests were conducted to investigate the mechanical behavior of UHPC tunnel lining segments thus produced. It was observed that the flow of UHPC mixtures decreased due to steel fibers addition, yet steel fibers increased the mechanical and durability properties. Flexural tests on lining segments showed that both the strain hardening (multiple cracking) and strain softening (post-peak behavior) phases were enhanced due to hybrid addition of steel fibers in comparison with the control segments without fibers. Specimens incorporating 3% of hybrid steel fibers achieved 57% increase in ultimate load carrying capacity and exhibited multiple cracking patterns compared to that of identical UHPC segments with 1% fibers. Moreover, segments without fibers incurred excessive cracking and spalling of concrete at the base under the thrust load test. However, more stable behavior was observed for segments incorporating steel fibers under the thrust load, indicating its capability to resist typical thrust loads during tunnel lining field installation. This study highlights the potential use of UHPC with hybrid steel fibers for improved structural behavior. Moreover, the use of UHPC allows producing structural members with reduced cross-sectional dimensions, leading to reduced overall structural weight and increased clear space.