Papers by Keyword: Limestone

Abstract: The purpose of the current investigation was to lower the CO₂ footprint of an industrial self-compacting concrete mix, which currently consists of CEMI 42.5R solely, without any natural pozzolanas or supplementary cementitious materials. The target compressive strength of the industrial mix needed to exceed 55 MPa at 28 days of curing. In the present study we attempted a 20% reduction of CEMI 42.5R (by total mass of solids) by adding 20% of limestone filler and subsequently added 1% of colloidal nanosilica, aiming (i) at leveraging strength loss due to the reduction of Portland cement, (ii) at providing early strength and (iii) at enhancing the microstructure. A water to binder ratio of 0.42 was selected and superplasticizers were added. Fresh properties were studied in terms of slump-flow test, density and 1-day strength. In addition, the 28 day compressive strength was also tested, meeting the mix design strength requirement. Interestingly, the slump flow was improved, indicating better packing effect, however the compressive strength of the control formulations was higher than that of the nanoenhanced formulation. Further insights are also provided.

Abstract: This article presents a study of the mechanical behavior of tuffeau, a porous building limestone. Previous studies were focused on using strain gauges for mechanical monitoring with some limited success due to the size and the local nature of the measurement. The Digital Image Correlation (DIC) method has proven to be a valuable tool for noncontact, full-field strain measurements in various materials, including rocks which are natural and heterogeneous materials. After a prior phase of optimization involving texture acquisition and lighting conditions, this paper compares several DIC software programs to achieve consistent results on soft limestone specimens. Once the DIC program is chosen, a focus is made on detecting heterogeneities in the stone specimens. The occurrence of such heterogeneities explains why strain gauge measurement sometimes fails when applied to soft and natural materials.

Abstract: Microwave heating was used with a gas foaming method for fabricating limestone carbonated hydroxyapatite scaffold (SCHA). Carbonated hydroxyapatite (CHA) was produced from limestone as a calcium source using the co-precipitation method. For further treatment, 0.6 gr CHA powder was mixed in 1 ml H₂O₂ solution as a blowing agent. The slurry-foam-like CHA was heated in a microwave with different levels of heating power from 180 W to 720 W. The SCHA samples were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and Scanning electron microscope (SEM). The crystallinity and crystallite size were affected due to different rates of heating power in the microwave-assisted method. The increasing temperature decreased the crystallite size from 37.49 to 33.97(nm). However, other crystallinity trends were observed at 180 W because the lower power heating needed a longer time to be formed SCHA. The different power rates have an insignificant contribution to the morphology of the scaffolds.

Abstract: The burning process of limestones is an important process in the modern industries, which can be described in two parts, CaCO₃ decarbonation due to the thermal stress and formation of CaO crystalline structure. It was already observed that the different composition and structure of a raw material influence the transformation process and has affect on the chemical and mechanical properties on the formed lime. This study is focused on the characterization of the raw material (porosity, chemical composition, geological age and origin) and its effect on the burning process and the formation of CaO and its properties. The microstructure of studied material burnt at different times of isothermal load was observed by SEM and the reactivity test was measured and analyzed. The limestone with a more porous inner system was burnt faster and is inclinable to overburn at longer thermal load.

Abstract: CaCO₃ is one of abundant minerals in nature, which is a promising material in thermochemical energy storage (TCES). In this work, we have succeeded in synthesizing CaCO₃/ZrO₂ composites by physical mixing with a magnetic stirrer using CaCO₃ from natural limestone. The mixing was carried out by mechanical stirring with various molar percentages of CaCO₃:ZrO₂ of 100:0, 85:15, 70:30 and 50:50. The phase and structure of the CaCO₃/ZrO₂ composites were characterized by x-ray diffraction (XRD). Thermal properties were characterized by thermogravimetri analyzer. Morphology of the composites was observed by scanning Electron microscopy (SEM) with energy dispersive x-ray (EDX). Based on the XRD results, the peak intensity of CaCO₃ at the crystalline plane of (104) decreased with increasing percentage of ZrO₂. The lattice volume of CaCO₃ also relatively decreases with increasing percentage of ZrO₂. The increase in the percentage of ZrO₂ in the CaCO₃/ZrO₂ composites makes the decomposition temperature also decreases. This is probably due to heat and mass transfer of ZrO₂.

Abstract: This study aims to produce and characterize CaO (calcium oxide) from limestone, a natural product of Lobong Village. Calcination is the thermal decomposition of limestone to remove carbon so that it can produce calcium oxide. One of the functions of CaO is as an eco-friendly catalyst that does not produce toxic or hazardous waste and can be reused. CaO resulting from the calcination process at a temperature of 900°C for 1.5 h was characterized using XRD, SEM, FTIR, and EDS. XRD analysis of calcined limestone produced 2θ (h k l) diffraction peaks, namely 32.228^o (1 1 1), 37.389^o (2 0 0), 53.864^o (2 2 0), 64.169^o (3 1 1), and 67.404^o (2 2 2) which indicates the dominance of CaO. SEM analysis shows that the morphological structure of Lobong limestone after calcination is more porous than before. Studies by FTIR show that the chemical bonds of carbonate groups in the calcined limestone are decreasing. EDS analysis also shows that the mapping of carbon, which forms carbonates in calcined limestone, is decreasing.

Abstract: The most of limestone objects in museums, storehouses and archaeological sites suffered from fragility and weakness which lead to the degradation of these artifacts. The present paper aims to evaluate the use of some nanolime-silica core-shell for consolidation process of these weak limestone artifacts. Two concentrations (5% and 10% w/w) were prepared for consolidating the aged limestone cubic samples. After complete drying, the cubic stones were exposed to the accelerated heat aging. The evaluation of consolidation process for the treated and aged treated samples was performed by some analytical methods such as measurement of physical properties and compressive strength. While, the investigation of surface morphology was carried out by scanning electron microscope (SEM) and measurement of contact angle. The characterization process for the prepared core-shell showed the smoothness and spherical shape of the grains with approximate size of 72 nm. The results of physical properties revealed that the treated samples with 10% of nanolime-silica core-shell gave the lowest porosity (15.57%) and water absorption (6.26%). Additionally, the treated samples with 10% concentration of nanolime-silica core-shell gave the highest values of compressive strength (21.23 Cm²/ Kg) and contact angle (122.78°). Moreover, the investigation using SEM revealed that the smoothness and good penetration for the treated sample with 10% concentration of nanolime-silica core-shell. The results of the present study revealed that the efficiency of consolidation process was maximum using 10% concentration of nanolime-silica core-shell and hence it was applied for consolidation of an archaeological limestone octagonal column, Egypt.

Abstract: This study investigates the effect of different types of local coarse aggregate, available in Saudi Arabia, on the strength of high-strength concrete. The utilized coarse aggregates are basalt and two different aggregates of limestone, denoted as limestone 1 and limestone 2. The results of 7 and 28 days compressive strength with different percentages of Micro Silica (MS) (i.e. range from 0 to 10%) show that the compressive strength of high strength concrete (HSC) is influenced by the type of coarse aggregate. Limestone 2 reaches the highest compressive strength followed by the types limestone 1 and then basalt. Properties of coarse aggregate influence the compressive strength of HSC, such as impact value (AIV), and texture. Also, the impact value variation between saturated surface dry (SSD) and dry conditions of the coarse aggregate affect significantly the compressive strength of HSC.

Abstract: Information about the lime composition used for the restoration of limestone is given. To develop a repair composition, a polysilicate solution was used. It has been established that polysilicate solutions contain a monomer, oligomer and polymeric varieties of silica. It was found by the molybdate method that the content of the polymeric form of silica γ-SiO₂ in the polysilicate solution is 15–19.93%, depending on the content of the silica sol. This composition of the polysilicate solution contributes to the manifestation of the high reactivity of silica. The technology for carrying out restoration work involves the application of a primer layer - liquid glass, followed by the application of a calcium chloride solution. After 20-30 minutes after applying the primer, it is possible to apply the repair composition with a spatula. It is shown that the use of a polysilicate solution in the formulation of a lime composition helps to increase the water resistance, adhesion strength of the composition to the base, and accelerates curing.

Abstract: Red mud (RM) is an industrial waste obtained from the Bayer process which is usually discharged into marine or disposed into a landfill causing pollution for the surrounding water, air, and soils. Thus, disposal of RM is an environmental concern, and it should be recycled effectively. Because RM consists of iron- and aluminum-rich phases, it is possible to be processed into cementitious material and utilized for construction purposes. This research fabricated a type of cement from the mixture of RM and limestone. The mixture was sintered at temperature of 1180 °C to obtain the clinker of the novel hydraulic cement with C₂S, C₃A, and C₄AF minerals. In which, C₂S, C₃A, and C₄AF are respectively belite, alite, and tetra-calcium aluminoferrite compounds that are characteristic hydraulic minerals of Portland cement clinker. The specifications of this cement were tested and evaluated in this study such as chemical and mineralogical compositions, fineness, specific surface area, mechanical strength after 3, 7, and 28 days.