Shape-Memory Materials

Geopolymers as an alternative to Portland cement: An overview

A generalized method to predict the compressive strength of high-performance concrete by improved random forest algorithm

This study investigates the effects of steel fiber and silica fume on the mechanical and fracture properties of ultra-high performance geopolymer concrete (UHPGC). Four volume fractions of steel fiber (0%, 1%, 2% and 3%) and four contents of silica fume by the mass of total binders (5%, 10%, 20% and 30%) were used. The mechanical and fracture properties evaluated include the compressive, splitting tensile and ultimate flexural strengths, modulus of elasticity, flexural behavior, fracture energy and stress intensity factor. In addition, the correlations among the compressive and splitting tensile strengths, and compressive strength and elastic modulus were studied. The results indicated the increase of steel fiber dosage resulted in the decrease of the workability, but the continuous improvement of mechanical and fracture performance of UHPGC. The empirical equations for predicting elastic modulus of conventional ultra-high performance concrete overestimated the elastic modulus of UHPGC, however some prediction formulas for the splitting tensile strength of PC-based concretes could be applied for UHPGC. Silica fume had a complicated influence on workability and hardened properties of UHPGC, which is strongly dependent on its amount. The inclusion of 10% silica fume induced the increase of the flowability, but the sharp degradation of the mechanical performance, while the specimens with 20% and 30% silica fume possessed the superior mechanical characteristic to that with 5% silica fume. The steel fiber dosage could be decreased without sacrificing the mechanical and fracture performance of UHPGC, via the increase of silica fume content.

Mechanical and fracture properties of ultra-high performance geopolymer concrete: Effects of steel fiber and silica fume

This study reports the development of ultra-high performance geopolymer concrete (UHPGC) and overcoming the brittleness feature of geopolymer matrix by using different steel fibers. Four straight steel fibers with different aspect ratios and two different deformed steel fibers were investigated. Flowability, compressive strength and flexural behavior including strengths and deflection, and energy absorption capacity of UHPGC, were systematically evaluated. A deformation ratio of steel fiber was introduced to quantitatively correlate the steel fiber shape and the mechanical performance. The flowability of fresh UHPGC mixtures decreased when the fiber content and length increased, as expected, and was inconspicuously influenced by fiber shape. The increase in fiber content and the decrease of fiber diameter contributed to the improvement of the mechanical strengths of UHPGC. The flexural behaviors of UHPGC improved as the fiber volume and length increased, while the compressive and first crack strengths were affected by both curing conditions and fiber dosages as well. Different from Portland cement-based composites, the corrugated fibers with a higher deformation ratio added in UHPGC, had an inferior strengthening and toughening efficiency, while for straight fibers, those longer and smaller in diameter were more preferred. Finally, based on the previous research, a new one with adjustment and simplification was proposed for that of newly-developed UHPGC, and the fitted results had higher correlation coefficients (r2).

Development of ultra-high performance geopolymer concrete (UHPGC): Influence of steel fiber on mechanical properties

Based on the principles of ultra-high performance concrete (UHPC) a Portland cement free, alkali-activated material was optimized in order to enhance strength and durability. The formulation is based on ground granulated blast furnace slag and as an activator a combination of potassium water-glass and potassium hydroxide was used. Furthermore, silica fume and metakaolin as inorganic fines were used to increase the packing density of the mixture. Quartz sand (0–2 mm) and quartz powder were added as aggregates. The results comprise an enhancement of the rheological properties by the stepwise increase of silica fume. A w/b ratio of less than 0.25 was realised using a certain mixing procedure with a high intensity mixer. The compressive strength reaches values comparable with the strength range of an UHPC. The already low capillary porosity could further be decreased by the substitution of slag with a small amount of metakaolin, which is leading to a higher polymerisation degree due to an incorporation of aluminium in the reaction products. The enhanced polymerisation degree was estimated by FTIR and XRD. Although no effective superplasticizer can be used in this high alkaline material, the low w/b ratio and a good workability can be achieved by using certain amounts of silica fume.

Influence of silica fume on properties of fresh and hardened ultra-high performance concrete based on alkali-activated slag

There is a common understanding that the environmental impacts of construction materials should be significantly reduced. This article provides a comprehensive environmental assessment within Life Cycle Assessment (LCA) boundaries for Ultra-High-Performance Concrete (UHPC) in comparison with Conventional Concrete (CC), in terms of carbon, material, and water footprint. Environmental impacts are determined for the cradle-to-grave life cycle of the UHPC, considering precast and ready-mix concrete. The LCA shows that UHPC has higher environmental impacts per m³. When the functionality of UHPC is considered, at case study level, two design options of a bridge are tested, which use either totally CC (CC design) or CC enhanced with UHPC (UHPC design). The results show that the UHPC design could provide a reduction of 14%, 27%, and 43% of carbon, material, and water footprint, respectively.

https://www.mdpi.com/1996-1944/12/6/851/pdf

Environmental Assessment of Ultra-High-Performance Concrete Using Carbon, Material, and Water Footprint

Influence of shrinkage and water transport mechanisms on microstructure and crack formation of tile adhesive mortars

Moisture induced length changes of tile adhesive mortars and their impact on adhesion strength

The rising number of failures of porcelain tiles, especially in outdoor applications, is to some extent a consequence of the critical combination of applying tiles of large dimensions and the non-porous nature of these tiles. A special setup allows a reproducible application of large-sized tiles (30 × 30 cm). In analogy to outdoor conditions, samples were stored under dry and wet conditions and have been investigated with different physico-chemical approaches. Under dry storage conditions adhesion strength is significantly lower along the periphery of the tiles compared to their centre. This reduction in adhesion performance is mainly caused by shrinkage of the mortar and substrate (∼0.1 mm/m). In situ observations through glass tiles indicate that the stresses induced by shrinkage are highest in the rim regions of the tiles. Under wet storage conditions, water percolates into the rim regions of the mortar, which leads to swelling of mortar and substrate, accelerating the delamination process. The findings of this study confirm observations on the construction site, where initial failures are often found at the periphery of large-sized tiles.

Alexander Wetzel

Papers

Influence of silica fume on properties of fresh and hardened ultra-high performance concrete based on alkali-activated slag

Environmental Assessment of Ultra-High-Performance Concrete Using Carbon, Material, and Water Footprint

Influence of shrinkage and water transport mechanisms on microstructure and crack formation of tile adhesive mortars

Moisture induced length changes of tile adhesive mortars and their impact on adhesion strength

Spatially resolved evolution of adhesion properties of large porcelain tiles