Halit Yazıcı

Mitigation of Detrimental Effects of Alkali-Silica Reaction in Cement-Based Composites by Combination of Steel Microfibers and Ground-Granulated Blast-Furnace Slag

The effect of combining brass-coated steel microfiber and ground-granulated blast-furnace slag (GGBS) on the mitigation of deleterious expansion due to alkali-silica reaction (ASR) was investigated in this research. A potentially reactive basaltic aggregate was chosen as a reactive material. Two series of specimens containing different amounts of microfiber were prepared. One of them was cured in 1 M NaOH solution at 80°C to obtain a similar maturity; the other series was cured in 80°C water up to 120 days. ASR expansion, strength development, and toughness properties were observed for 120 days in NaOH solution and the results were compared with specimens kept in water. Test results indicate that the combination of GGBS and steel fibers reduced ASR expansion significantly. Furthermore, the combination was very effective at preventing the mechanical property loss due to ASR, such as flexural strength, compressive strength, and toughness. Microstructural investigations revealed that the reaction products had a different morphology (e.g., fibrous, network appearance) when the specimens were kept in NaOH solution.

Improvement on SIFCON Performance by Fiber Orientation and High-Volume Mineral Admixtures

The effects of steel fiber alignment and high-volume mineral admixture replacement [Class C fly ash (FA) and ground granulated blast furnace slag (GGBS)] on the mechanical properties of SIFCON (Slurry Infiltrated Fiber Concrete) have been investigated. Ordinary portland cement was replaced with 50% (by weight) FA or GGBS in SIFCON slurries, and two different steel fiber alignments (random and oriented in one direction) were used. Test results showed that FA and GGBS replacement positively affected mechanical properties (compressive and flexural strength and fracture energy) and fiber alignment is an important factor for superior performance. Binary combination of improved matrices (low water/binder ratio and mineral admixture replacement) and proper fiber orientation enhances mechanical performance, particularly flexural properties of SIFCON. Flexural strength and fracture energy of this composite are 138 MPa and 195,815 N/m, respectively. Scanning electron microscope investigations revealed tobermorite-like structures having different morphology such as foiled, fibrous, and honeycomb with low Ca/Si ratio after autoclaving. Mercury porosimeter tests showed the decreasing of total porosity and pore refinement with FA or GGBS.

Effect of Aggregate Type on Mechanical Properties of Reactive Powder Concrete

This aricle focuses on the experimental study of the mechanical properties of reactive powder concrete (RPC) that is produced with different aggregates, such as korund, basalt, limestone, quartz, sintered bauxite, and granite. The effects of aggregate type on mechanical properties were investigated under standard, atmospheric, and high-pressure steam curing in this article. The test results indicate that very high compressive strength can be achieved even with low-strength or smooth-surface aggregates; however, superior flexural performance requires high-strength aggregate with rough surface characteristics. A compressive strength of approximately 200 MPa (29 ksi) can be obtained when strong and rough-surface textured aggregate were used under standard curing conditions. Atmospheric and high-pressure steam curing improved the compressive strength significantly. These curing regimes, however, did not considerably improve the flexural performance. Pressure application in fresh state resulted in a great improvement of the compressive strength of RPC, particularly in the case of high-strength and rough-surface textured aggregates. In this way, a compressive strength over 400 MPa (58 ksi) was obtained with bauxite aggregate after pressure application and autoclaving.

Effect of early-age freeze-thaw exposure on the mechanical performance of self-compacting repair mortars

Abstract Self-compacting repair mortar (SCRM) is a functional material for repair or retrofit applications. Industrial byproducts, such as fly ash (FA) or ground granulated blast furnace slag (GGBFS), can be used to reduce cement dosage and to obtain an eco-friendly material. However, these waste materials may cause durability problems at early ages as a result of curing sensitivity. In this study, the effects of high-volume FA and GGBFS replacement on early-age freeze-thaw (F-T) resistance of SCRM with and without steel microfibers were investigated. The mechanical properties, including fracture energy, were determined after F-T cycles. The fresh state properties and volume stability of the hardened specimens were studied. The results demonstrated that prolonged curing is essential to avoid the loss in mechanical properties due to F-T exposure. SCRM containing high-volume byproducts seem vulnerable to the effect of F-T at early ages, and this negative effect cannot be overcome with steel microfibers.

Transport properties and freeze-thaw resistance of mortar mixtures containing recycled concrete and glass aggregates

The effects of recycled glass (RG) and recycled concrete (RC) fine aggregates on the compressive strength, ultrasonic pulse velocity, dynamic elastic modulus, transport properties and freeze–thaw resistance of mortar mixture were investigated comparatively. Nine different mortar mixtures were prepared by partial replacement of crushed-limestone fine aggregate with recycled aggregates. Compared to that of the control mixture, the transport properties of RC aggregate-bearing mixtures inversely affected with increasing the replacement level of this aggregate. The opposite results were obtained in RG aggregate-containing mixtures. Frost resistance of mortar mixture improved by using both of the recycled aggregates. Improvement of frost resistance of RC mixtures was attributed to the presence of improved Interfacial transition zone between matrix and coarse aggregate (ITZ) in RC-bearing mixture and to the high number of pores existing in the well-distributed RC aggregates in the mixture. Perhaps, these pores provide additional sites for the water escaped from capillary pores upon ice formation.