Andrzej Cwirzen

Effects of Reactive Magnesia on Microstructure and Frost Durability of Portland Cement–Based Binders

AbstractThe effects of portland cement (PC) replacement with magnesia (reactive magnesium-oxide) on properties of PC-based pastes, mortars, and concretes were investigated. The research included determination of mechanical properties and frost durability in addition to studies of the microstructure and microchemistry. The mortar and paste mixtures contained from 10–80 weight percent (wt%) replacement of PC by magnesia and had water to cementitious-binder ratios from 0.4–0.7, whereas concretes contained from 5–10xa0wt% magnesia and had a water to cementitious-binder ratio of 0.53. Replacement of PC by magnesia had adverse effects on the mechanical properties and frost durability. The magnesia reduced microcracking of the binder matrix in comparison with pastes containing only PC. The primary hydration product of magnesia was brucite in addition to regular hydration phases of PC. The amount of formed portlandite was increased. Magnesia caused densification of the microstructure but also increased the capillar...

Effect of Baltic Seawater and Binder Type on Frost Durability of Concrete

AbstractThe effects of Baltic seawater on frost durability of PC concretes using sulfate resistant portland cement and combination of rapid hardening portland cement with silica fume were studied. The freeze-thaw cycles were performed on specimens exposed to the Baltic seawater, 3% sodium chloride solution and deionized water. The freeze-thaw cycles appeared to cause the most extensive internal damage in specimens based on sulfate resistant cement (SR) and exposed to seawater. The most extensive surface scaling was observed in the case of concretes containing silica fume and exposed to deicing salts. Based on the thermo gravimetric and X-ray diffraction analyses it was concluded that extensive internal damage of concrete based on SR was caused by changes of the microstructure due to secondary formation of ettringite, carbonation, and formation of calcite. The results showed also that low C3A content of the SR did not fully mitigate formation of secondary ettringite during freeze-thaw cycles. A combination...

Formation of Lignin Nanoparticles by Combining Organosolv Pretreatment of Birch Biomass and Homogenization Processes

Valorization of lignocellulosic biomass into a biorefinery scheme requires the use of all biomass components; in this, the lignin fraction is often underutilized. Conversion of lignin to nanoparticles is an attractive solution. Here, we investigated the effect of different lignin isolation processes and a post-treatment homogenization step on particle formation. Lignin was isolated from birch chips by using two organosolv processes, traditional organosolv (OS) and hybrid organosolv-steam explosion (HOS-SE) at various ethanol contents. For post-treatment, lignin was homogenized at 500 bar using different ethanol:water ratios. Isolation of lignin with OS resulted in unshaped lignin particles, whereas after HOS-SE, lignin micro-particles were formed directly. Addition of an acidic catalyst during HOS-SE had a negative impact on the particle formation, and the optimal ethanol content was 50–60% v/v. Homogenization had a positive effect as it transformed initially unshaped lignin into spherical nanoparticles and reduced the size of the micro-particles isolated by HOS-SE. Ethanol content during homogenization affected the size of the particles, with the optimal results obtained at 75% v/v. We demonstrate that organosolv lignin can be used as an excellent starting material for nanoparticle preparation, with a simple method without the need for extensive chemical modification. It was also demonstrated that tuning of the operational parameters results in nanoparticles of smaller size and with better size homogeneity.

Activation of a Raw Clay by Mechanochemical Process—Effects of Various Parameters on the Process Efficiency and Cementitious Properties

The efficiency of the mechanochemical activation (MCA) is influenced by various process parameters as well as by the properties of the treated material. The main objective of this research was to optimize the MCA process, gaining enhancement of the chemical reactivity of a Swedish raw clay, which is going to be used as an alkali-activated cementitious binder. The effects of the amount of water, the filling ratio, the rotation speed, and the grinding duration on the amorphization degree were evaluated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Generally, wet and dry processes showed an extensive amorphization of both kaolinite and muscovite minerals present in the studied clay. On the contrary, quartz was amorphized mainly by the wet grinding process. The efficiency of both dry and wet grinding processes was enhanced by the increased number of grinding media versus the amount of the activated material. However, longer processing times caused significant agglomeration while a higher rotational speed enhanced the amorphization. Preliminary tests have shown that alkali activation of the processed clays produced hardened samples. Furthermore, the increased amorphization corresponded to the increased compressive strength values.

Bond Strength between Glass Fiber Fabrics and Low Water-to-Binder Ratio Mortar: Experimental Characterization

Full utilization of mechanical properties of glass fiber fabric-reinforced cement composites is very limited due to a low bond strength between fibers and the binder matrix. An experimental setup was developed and evaluated to correlate the mortar penetration depth with several key parameters. The studied parameters included fresh mortar properties, compressive and flexural strengths of mortar, the fabric/mortar bond strength, fabric pullout strength, and a single-lap shear strength. Results showed that an average penetration of mortar did not exceed 100u2009µm even at a higher water-to-binder ratio. The maximum particle size of the used fillers should be below an average spacing of single glass fibers, which in this case was less than 20u2009µm to avoid the sieving effect, preventing effective penetration. The pullout strength was strongly affected by the penetration depth, while the single-lap shear strength was also additionally affected by the mechanical properties of the mortar.