Serdar Aydın

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.

Engineering Properties of Reactive Powder Concrete without Portland Cement

This paper reports the properties of a new type of high-performance composite material developed as an alternative construction material to reactive powder concrete (RPC) with a compressive strength over 200 MPa (29.0 ksi). This composite has been developed by the activation of slag and silica fume, without using portland cement. A comparative experimental study on the mechanical properties, microstructure, fresh-state properties, leaching of ions, bond to steel, and dimensional stability of RPC produced with portland cement (CRPC) and alkali-activated cement (ARPC) has been implemented. Test results show that ARPC has a very different microstructure with a great number of nano-sized pores compared to CRPC. Although these two RPC mixtures have similar compressive strength values, ARPC has significantly higher flexural performance, fracture energy, and bond to steel compared to CRPC. ARPC composites seem to be a good alternative to CRPC because of these superior properties and reduced environmental problems.

Flexural Performance of Alkali-Activated Slag Cements under Quasi-Static and Impact Loading

AbstractEffects of silicate modulus (Ms) of an activator solution and the matrix components of alkali-activated slag cement (AASC) on the flexural parameters of AASC mortars were investigated under static and low-velocity impact loadings. AASC mixtures in two different Ms (SiO2/Na2O) ratios were prepared by the partial replacement of ground granulated blast-furnace slag (GGBFS) with fly ash (FA), metakaolin (MK), and silica fume (SF). Impact load was generated by a free-fall of a hammer onto the simply supported notched beams from different heights. Test results showed that SF-incorporating AASC had similar impact resistance to the control AASC mixture at all tested velocities while the MK-incorporating AASC had significantly lower impact resistance with an Ms ratio of 0.8. The increase of Ms ratio had a profound effect only in the MK series. The dynamic increase factors (DIF) in AASC mixtures increased with impact velocity. Dynamic increase factors were found to be higher in the AASC mixtures having poro...

Development of a Proper Mix-Design for Impact Loading of Deflection Hardening Hybrid Fiber Reinforced Concrete

This study aims to develop a low-cost Hybrid Fiber Reinforced Concrete (HyFRC) that exhibits deflection hardening behavior under bending and has high energy absorption capacity under impact loading by determining proper combination of steel and polyvinyl alcohol (PVA) fibers. More than forty mixtures were prepared including two mixtures of conventional concrete, six mixtures of Engineered Cementitious Composites (ECC), and thirty-six mixtures of HyFRC. The design parameters were chosen as fly ash to cement ratio (1.2, 1.7 and 2.2), steel fiber type and amount (0.5%, 0.75%, and 1.25% by volume), PVA fiber amount (0.25% and 0.50% by volume), and maximum aggregate size (Dmax) of 8 mm and 16 mm. Several tests were carried out on fresh and hardened specimens such as bending, compression, and low-velocity flexural impact loading. Based on the results, it is found that the mixture with 0.75% steel fiber and 0.25% PVA showed the best performance for the aim of the study.