Production of an eco-friendly concrete by including high-volume zeolitic supplementary cementitious materials and quicklime.

The production of ordinary Portland cement (OPC) is one of the main global causes of CO2 release to the atmosphere. However, its availability and unique characteristics as a binding material make it difficult to be substituted by eco-friendlier materials. However, OPC partial replacement with pozzolanic materials is one of the best solutions to this problem. Hence, in this study, various types of high-volume zeolite were employed as supplementary cementitious materials (SCM), substituting the OPC by up to 50 wt.% in the composition of the created mortars. Besides, quicklime and inorganic accelerators were included in some of the mortar mixtures to improve the hydration reaction and enhance its speed. The mechanical, durability and durability in sea water properties were investigated. Although the usage of SCM caused a decrease in the mechanical and durability properties of the specimens, the addition of 10 wt.% quicklime palliated this degradation by enhancing by 40% the 28-days compressive strength of the specimens and by significantly improving their durability (porosity, freeze-thaw resistance and carbonation resistance). Moreover, the mixtures were proved to be resistance to aggressive ionic environments, since their compressive strength even increased after 28-day immersion in seawater, due to the additional formation of hydration compounds.

The Influence of Expanded Glass and Expanded Clay on Lightweight Aggregate Shotcrete Properties.

In the construction industry, the selection of sustainable materials leads to a movement towards more sustainable construction. In this study, lightweight aggregate shotcrete based on expanded glass (EG) and expanded clay (EC) is investigated. The goal of the study is to determine the influence of EG and EC inclusion on the properties of shotcrete. Ordinary Portland cement (OPC) powder with supplementary cementitious materials, such as silica fume and ground glass waste, are used as binders. The mechanical, physical and morphological properties, as well as the mineral and oxygen compositions, are obtained through compressive and flexural strength tests, thermal conductivity measurements, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. In this study, the mechanical, physical and thermal properties and waste utilization as cement supplementary materials are balanced. The shotcrete samples show that a density of 790 kg/m3 had a good thermal performance (thermal conductivity coefficient of 0.174 W/(m·K)) with the sufficient compressive strength of 6.26 MPa.

The Using of Concrete Wash Water from Ready Mixed Concrete Plants in Cement Systems.

Concrete plants accumulate large amounts of concrete wash water. This water, which pH is highly alkaline, has a negative impact on the environment. Its reuse in fresh concrete slightly reduces its mechanical properties. The combination of concrete wash water and zeolitic by-product led to an increase of 4.6% in the compressive strength at 7 days hydration and up to 30% at 28 days hydration. The same combination led to the denser microstructure compared to the samples made with concrete wash water. This could be explained by the pozzolanic reaction of the zeolitic by-product. The complex chemical reactions of cement, zeolitic by-product, and fines presented in the concrete wash water occurred. Therefore, it was suggested the reusing method of concrete wash water together with zeolitic by-product in the fresh concrete mixtures by substituting some amount of tap water with concrete wash water. In this way, the consumption of tap water is possible to reduce in cement systems.

Preparation of Sorbents Containing Straetlingite Phase from Zeolitic By-Product and Their Performance for Ammonium Ion Removal.

In this study, straetlingite-based sorbents were used for NH4+ ion removal from a synthetic aqueous solution and from the wastewater of an open recirculation African catfish farming system. This study was performed using column experiments with four different filtration rates (2, 5, 10, and 15 mL/min). It was determined that breakthrough points and sorption capacity could be affected by several parameters such as flow rate and mineral composition of sorption materials. In the synthetic aqueous solution, NH4+ removal reached the highest sorption capacity, i.e., 0.341 mg/g with the S30 sorbent at a filtration rate of 10 mL/min and an initial concentration of 10 mg/L of NH4+ ions. It is important to emphasize that, in this case, the Ce/C0 ratio of 0.9 was not reached after 420 min of sorption. It was also determined that the NH4+ sorption capacity was influenced by phosphorus. In the wastewater, the NH4+ sorption capacity was almost seven times lower than that in the synthetic aqueous solution. However, it should be highlighted that the P sorption capacity reached 0.512 mg/g. According to these results, it can be concluded that straetlingite-based sorbents can be used for NH4+ ion removal from a synthetic aqueous solution, as well as for both NH4+ and P removal from industrial wastewater. In the wastewater, a significantly higher sorption capacity of the investigated sorbents was detected for P than for NH4+.

Conversion of silica by-product into zeolites by thermo-sonochemical treatment.

The fine powdered silica by-product of processing of aluminum fluoride (fertilizer plant, Lithuania) was used for zeolite synthesis as silica and aluminum source. The effect of sonication time and the time of hydrothermal synthesis on crystallinity of the synthesized zeolite were studied. This allowed the transformation of the by-product to the mixture of Na-P zeolite and Na-X zeolite. It was determined that ultrasonic-assisted hydrothermal action effected the "diamond" shape formation of Na-P zeolite with clear crystal edges. Na-P zeolite had the morphology of pseudo-spherical forms constituted by small plates when hydrothermal treatment (without sonication) was use for the preparation of zeolites. Moreover, it was determined that ultrasonic-assisted hydrothermal method effected a reduction in the crystal size compared with the zeolites which were synthesized only by using hydrothermal synthesis. The total amount of zeolites as high as 88-93% was achieved after 24 h of hydrothermal treatment followed or unfollowed by sonication. By using longer duration (20 min) of ultrasound pretreatment it is possible to reduce the duration of hydrothermal synthesis: from 24 h to 12 h of hydrothermal treatment. In this case, similar results of total amount of zeolites were detected. In the present work, low-cost raw materials, such as silica by-product have been investigated for the production of zeolites.

Removal of ammonium ion from aqueous solutions by using unmodified and H2O2-modified zeolitic waste.

In the petroleum industry during a catalytic cracking process, the used zeolitic catalyst becomes waste. This article investigated the sorption capacities of ammonium ions from aqueous solutions onto the previously mentioned zeolitic waste by batch experiments. Three types of zeolitic waste were used: unmodified zeolitic waste with two different particle size distributions and H2O2-modified zeolitic waste. Several techniques, including X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) multilayer adsorption theory measurements, and X-ray fluorescence analysis (XRF) were used to demonstrate experimentally that the zeolitic waste could be used as a sorbent for the water decontamination of NH4+ ions. The morphology of zeolitic waste investigated by scanning electron microscopy (SEM) revealed particles with a spherical shape. The nitrogen adsorption-desorption isotherms showed an isotherm mixture of types I (pure microporous) and IV (mesoporous). This suggested that the investigated zeolitic materials were mesoporous (4.84 nm) and microporous (0.852 nm), as well as containing slit/cylindric pores, according to a quench solid density functional theory (QSDFT) adsorption branch model. Zeolitic waste from the oil industry showed good NH4+ sorption properties (removal efficiency of 72%), thus becoming a potential adsorbent to be used in the treatment of contaminated aqueous effluents polluted with ammonium ions. Simultaneous waste and water decontamination can be achieved, providing a new tool and enhanced capabilities for environmental remediation.

Effects of ultrasonic treatment on zeolite NaA synthesized from by-product silica.

The synthesis of zeolite NaA from silica by-product was carried out in the presence of 20 kHz ultrasound at room temperature. Zeolites obtained in this type of synthesis were compared to zeolites obtained by performing conventional static syntheses under similar conditions. The sonication effects on zeolite NaA synthesis were characterized by phase identification, crystallinity etc. The effects of different parameters such as crystallization time and initial materials preparation methods on the crystallinity and morphology of the synthesized zeolites were investigated. The final products were characterized by XRD and FT-IR. It was possible to obtain crystalline zeolite NaA from by-product silica in the presence of ultrasound.