Burnt Limestone Research Articles

Silica fume activated by NaOH and KOH in cement mortars: Rheological and mechanical study

Ordinary Portland cement (OPC) is the most used binder in the world, applied in practically all phases of the building. The problem is that this binder is highly harmful to the environment due to its production stage, which involves clinkerization by burning limestone. In this context, the objective of this work was to evaluate the potential of using silica fume as a partial substitute for cement, however verifying its activation potential. Silica fume is widely used as a pozzolanic material. In this work, the use of the material as alkali cement activated with sodium and potassium hydroxide (NaOH and KOH) was tested. The methods used consist of producing mortars in the compositions 1:3:0.60 (OPC: natural sand: water) and replacing the OPC with silica fume (10 and 20%) in three ways: i) without activation, as a pozzolanic material; (ii) activated by NaOH; and (iii) activated by KOH. Cylindrical specimens measuring 50x100 cm were produced, containing 0, 10 and 20% silica fume replacing OPC. Properties were evaluated in the fresh state, such as depth of penetration, consistency and squeeze flow, and tests in the hardened state, such as water absorption, density, and compressive strength. The results in the fresh state indicate that the compositions containing NaOH accelerate the setting process, but without impairing the workability of the mortar before the hardening process. The results of the fresh state of the compositions containing KOH indicate that the dissolution of this material is not as efficient in the cement medium in the first minutes after mixing the material. This impairs the workability of the mortar. In the hardened state, the density and water absorption results showed the occurrence of alkaline activation of silica fume. The results of compressive strength and diametral compressive strength were better for the compositions with NaOH and KOH, due to the occurrence of alkaline activation of silica fume which provided the formation of tobermorite and zeolites. Therefore, as an improvement this work concluded that the use of hydroxides together with the pozzolanic material silica fume is a more efficient way of replacing OPC than the isolated use of pozzolan, due to the occurrence of the alkaline activation process.

Investigation of Excessive Wear of Ashaka Coal Mill Riser Duct and Idendifying the Optimum Solution

Cement plants use fuel in burning limestone to make clinker in kilns. Due to high cost of fuels, most Cement plants are changing from high-cost liquid fuel like heavy fuel to cheap solid fuel like coal. Ashaka adopt the later. The coal is first pulverised in a ball mill and leaves the mill through a riser duct by pneumatic transport before been used in the kiln as fuel. The riser duct undergoes excessive wear which result in frequent downtime and affect the intendent purpose of fuel substitution. Also, the pulverised coal escaping under pressure through eroded areas on the duct increase the risk of fire and reduce the overall safety of the workshop. Current method which involved patching the duct by welding fail to solve the problem. This work investigates the root cause of the frequent wear of the riser duct by checking the abrasiveness of the coal being transported, checking the effect of the duct profile on wear through simulation using computational fluid dynamics (CFD). Checking the duct material rate of wear and providing the best solution in terms of cost and feasibility. After simulation using CFD it was revealed that the duct profile contributed to the wear rate. Since changing the profile will be costly, a different solution approach was considered i.e., surface finishing. Different Material samples suggested to be used as surface finishing on the duct were tested for wear at different angles using an abrasive test equipment. The test equipment which conforms with ASTM was designed, simulated using CFD and constructed. The best material with good wear resistance was found to be galvanised steel coated with automobile anti gravel and grounded with P1000. Coating the internal of the riser duct with the above material is considered to be the optimum solution in terms of cost and feasibility.

Effect of nanoclay and burnt limestone powder on fresh and hardened properties of self-compacting concrete

The growing rate of cement production and construction waste due to rapid urbanization is producing environmental threat. Therefore, it is necessary to replace fully or partially with reinforcement material. Thus, in this research work, sulfate resistance cement (SRC) was replaced with different weight percentages of nanoclay (NC) (2, 4 and 6%) and burnt limestone powder (BLP) (50, 75 and 100 kg) to produce self-compacting concrete (SCC) for investigating the fresh and hardened properties. The local Iraqi natural Kaolin clay was calcinated at 700 °C for 2 h and milled for 40 h through ball milling to produce NC. Further, the limestone powder was burnt at 700 °C for 2 h and partially replaced with SRC. The ball milling successfully reduced clay to a particle size of < 75 nm sized for NC. Moreover, the inclusion of NC and BLP significantly affected the fresh properties of SCC. For hardened properties, the inclusion of both mixtures gradually increased hardened properties; however, the NC-incorporating SCC specimens have higher hardened properties than reference SCC (SCC0), whereas the lower weight percentages of BLP provided insignificant hardened properties. Additionally, as based on results, both mixture material (NC and BLP) can be utilized for producing SCC.

Ramped pyroxidation: A new approach for radiocarbon dating of lime mortars

Current methodologies for radiocarbon dating of mortars typically use mechanical and chemical separation to isolate fractions of carbon dioxide from suitable lime binder carbonates. These methods have a moderate frequency of success, but difficulties are often encountered with (a) secondary crystallisation, (b) the presence of incompletely burnt limestone or limestone aggregate, and (c) more complex hydraulic mortars (e.g. pozzolana or cocciopesto mortars). An alternative approach to isolating CO2 from mortar involves thermal decomposition of the sample.A new ramped pyroxidation (RPO) facility has recently been constructed at the 14CHRONO Centre. In RPO, samples are incrementally heated, with CO2 produced as the sample undergoes thermal decomposition in the presence (oxidation) or absence (pyrolysis) of oxygen. The CO2 evolved from different temperature fraction are collected cryogenically and radiocarbon dated. This method was applied to several lime mortars with expected ages to investigate if CO2 fractions only associated with the setting of the lime binder could be isolated.For all samples tested, positive results were obtained. All but the first of six CO2 fraction taken during the earlier stages of thermal decomposition were in statistical agreement and could be combined to provide an age that was in excellent agreement with the expected ages (for an Irish medieval round tower, and for a Finnish medieval castle and church). The lowest temperature fraction, not in statistical agreement, is significantly earlier and attributed to contamination from charcoal or coke from lime production. Positive results were also obtained from a piece of mortar that had undergone no pre-treatment.Modelling examining the potential of RPO to isolate lime binder CO2 fractions, where either limestone (or incompletely burnt limestone) or secondary re-crystallised calcite are present as contaminants, further demonstrate the suitability of the approach.

A 10,400-year-old sunken lime kiln from the Early Pre-Pottery Neolithic B at the Nesher-Ramla quarry (el-Khirbe), Israel

The Pre-Pottery Neolithic B (PPNB) is the first period in human cultural evolution that is characterized by the extensive production of lime plaster for architectural, decorative and ritual purposes. The production of large quantities of lime plaster requires the operation of a lime kiln, a structure where limestone cobbles are heated to high temperatures (>600°C) to obtain quicklime, which is then mixed with water to form a moldable lime putty. However, little is known about lime kilns and plaster production processes during the PPNB. This may be because the technology used at that time was simple and left few traces that are unique to lime plaster production. These include combustion features rich in lime plaster and heat-altered sediments, which are difficult to identify through only a visual inspection of the archaeological context. Here we report the study of a small sinkhole at the Nesher-Ramla quarry in Israel, which yielded Early PPNB artifacts. Using infrared spectrometry and micromorphology of sediments, we identified in-situ deposits of heat-altered sediments rich in fragments of burnt limestone, lime plaster, and wood ash in the form of charcoal, phytoliths and siliceous aggregates, which are features consistent with the operation of a lime kiln. Charred botanical remains were characterized and used for radiocarbon dating, which determined the age of the site at 10,400cal BP. We therefore conclude, based on the examination of the microscopic archaeological record, that this sinkhole was used as a lime kiln during the Early PPNB.

Heat release during the hydration of calcinated α-C2SH and its mixture with killalaite

In this work, the influence of the mineral composition of the synthesized calcium silicate hydrates on their hydraulic activity after thermal treatment was determined. Primary mixture, consisting of quartz sand and burnt limestone (CaO/SiO2 = 2), was treated hydrothermally with NaOH additive at 200 °C. It was determined that α-C2SH prevailed in the product after 4 h of the synthesis. The results of DSC and XRD analysis revealed that α-C2SH was partially decomposed after 12 h of the synthesis and newly formed compounds were identified—killalaite, portlandite and C–S–H. The products of 4 and 12 h synthesis were treated thermally at temperatures between 450 and 1000 °C. It was determined that dellaite and x-C2S formed already at 450 °C, β-C2S at 600 °C and α′L-C2S at 800 °C when the 4 h synthesis product, in which α-C2SH prevailed, was treated thermally. On the other hand, killalaite remained stable up to 600 °C, and the temperature values, at which mentioned calcium silicates formed, increased in case of a 12 h synthesis product. Heat flow values of the main hydration reaction and total heat release exceeded 3.1 mW g−1 and 140 J g−1 accordingly in case of the samples in which α-C2SH prevailed. However, increase in the thermal treatment temperature resulted in a decrease in the mixtures hydraulic activity. It was proved that killalaite formation in the product of the 12 h hydrothermal synthesis vividly decreases its hydraulic activity after the thermal treatment in the temperature range of 450–1000 °C. No increment in the heat flow values that could be attributed to the main hydration reaction (acceleration period) was witnessed in all the curves of the heat flow analysis in this case.

Shedding light onto the spectra of lime: Raman and luminescence bands of CaO, Ca(OH)2 and CaCO3

In microscopy studies of 19th‐century cement stone, we found free lime in the form of darkened spherical structures, as they were described in the literature already. When trying to determine their phase composition by Raman spectroscopy, we encountered contradictive assignments in literature spectra of the lime phases CaO, Ca(OH)2 and CaCO3 and observed strong spectral features that have been ignored or erroneously assigned so far. In this study we present Raman spectra of pure lime phases and of a naturally grown calcite crystal, burnt limestone (quick lime, mainly CaO), aged slaked lime putty (mainly Ca(OH)2), and carbonated lime putty (mainly CaCO3). Based on the results, we shed light mainly onto these two questions: (1) Does CaO have a Raman spectrum? (2) Which features in the spectra are luminescence bands that could be (and already have been) misinterpreted as Raman bands? We proof our assignment of luminescence bands in lime phases by using three different laser wavelengths for excitation, and give hypotheses on the origin of the luminescence as well as practical advices on how to identify these misleading features in Raman spectra. This article is mainly addressed to users of Raman spectroscopy in different fields of material analysis who might not be aware of the presence of interfering bands in their spectra. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Identification, Extraction, and Preparation of Reliable Lime Samples for 14C Dating of Plasters and Mortars with the “Pure Lime Lumps” Technique

Radiocarbon dating was first applied to historic lime mortars during the 1960s. However, despite the relative simplicity of the technique in principle, a number of subsequent studies have highlighted important aspects that should be considered. One of the most significant of these challenges arises from sample contamination by carbonaceous substances such as incompletely burnt limestone and aggregates of fossil origin containing “dead” 14C. More recent studies have shown that in the majority of old lime-based mixtures the contamination problem can be avoided through selection of pure lime lumps. These particular types of lumps are believed to originate from areas where the lime is incompletely mixed with the aggregate. It has been demonstrated that even a single lime lump can provide sufficient material for a 14C date of the mortar from which the lump was taken (Pesce et al. 2009). This paper describes the practical challenges associated with location, extraction, and preparation of 4 lime lumps extracted from 2 new sites for 14C dating. These include distinguishing the lime lumps from other lumps present in the matrix and the removal of material surrounding the lime lump. The coherence of 14C dating with other archaeological information on the chronology of historic sites is highlighted through case studies.

Methods for the efficient use of the gas energy from shaft ferroalloy electric furnaces

The average values of these efficiencies are as follows: η t = 0.5‐0.7 and η e = 0.90‐0.95. At η f = 0.45‐ 0.66, the energy lost by radiation from the furnace top, furnace jacket, and electrode surfaces; by cooling water and air; and, most importantly, by the physical heat of the waste gases is at least 30‐50%. The chemical energy of the waste furnace gases (ferrogases) is a substantial source for the compensation of the heat losses in ferroalloy furnaces and, hence, for electric energy saving. It was theoretically found and experimentally supported that the gas products of the reduction reactions occurring in the working space of shaft furnaces contain a significant amount of the gas components (CO, H 2 , CH 4 ) that have a high calorific value (CV) [1]. The problem of the efficient utilization of the ferrogas energy has not been adequately elucidated in available works. There are different data on the use of a ferrogas in a mixture with natural gas in furnaces for burning limestone. Powerful (more than 60 MW) foreign-made furnaces for making ferromanganese and ferrochromium have a system for reburning a ferrogas in the mounted bins where the initial charge is heated [2]. We estimated the chemical energy of the gases accompanying the slag-free and slag processes in 16.5‐ 75 MV A furnaces (table). The calorific value (kcal/m 3 ) was calculated by the formula ηf ηtηe,

Effect of burning conditions on properties of artificial hydraulic lime mortar obtained from limestone and siliceous waste materials

The present study was carried out to produce an artificial hydraulic lime for repair and conservation of historic masonry. Lime mortar is preferred to cement based mortar for conservation work because it is more compatible with stone and ancient brickwork, as well as being a more sustainable material. The study focused on the effect of burning conditions on the properties of an artificial hydraulic lime mortar obtained by burning limestone and siliceous waste materials. The raw meals were prepared from five types of siliceous materials obtained as byproducts from industrial processes (pulverised fuel ash, glass cullet, silica sand, crushed rock and spent oil shale) with the amount of silica between 3 and 16%. The raw meal was burned in an electric furnace at 975°C for 3 h. The mortar was prepared by mixing hot slaked lime putty (water/lime ratio ∼1.6) and 'Gowrie' sand at a lime/sand ratio of 1 : 3 by weight. The limes and lime mortar were prepared and tested according to BS EN 459-2:2001. The investigations carried out on the products included free lime analysis, strength test and microstructural examination. The results show that the glass cullet lime is the most hydraulic product and can be classified as feebly hydraulic. It suggests that this hydraulic lime could be produced using a traditional kiln at a low cost.

HISTORICAL LIME PRODUCTION IN SOUTHEASTERN ARIZONA

The production of lime by burning limestone has been practiced in the Americas for at least 6,000 years and beginning in Spanish Colonial times was an important cottage industry in southern Arizona. Lime kilns, however, have largely been overlooked, ignored, or avoided by archaeologists and historians alike. Their excavation is uncomfortable and often relatively fruitless, yielding architectural data but little to suggest when a kiln was operated, or by whom. Archival data are also often lacking because kilns were constructed in areas of optimum resources, with little effort to secure ownership of the land. This article reviews historical lime production in southern Arizona with a focus on the Tucson Basin.

Chestnut Grove: An Early 19th-Century Lime Burning Industry in the Connecticut Western Reserve

Information is limited regarding the development of early industries along Lake Erie's northeastern shore of the Connecticut Western Reserve. With the opening of the Ohio Country, farmers and pioneer industrialists found the virgin land abundant with natural resources and ready to be exploited. Evidence derived from a rescue excavation of a stone structure at the outlet of the Cowles Creek together with documents established the presence of a lime burning industry. Early settlers found a plentiful wood supply located on the mainland which provided the necessary fuel for burning limestone mined on Cunningham (Kelleys) Island and permitted the construction of shops for use on Lake Erie. Some of the ships that were constructed locally were used to transport lime for the industry. The Sandusky Bay Islands eventually became a rich source of limestone for the expanding American consumer market.

Determining the coefficients of air consumption from volumetric analysis of flue gases during the breakdown of material being calcined

A formula is proposed for determining the quantity of carbon dioxide evolved from material being burnt (dolomite, magnesite, or limestone) per 1 kg or 1 Nm3 for fuel, and also a formula for determining the coefficient of air consumption during the combustion of any fuel in the presence or absence, within the combustion products, of gases from the material being broken down (CO2).

Ancient Mesoamerican Mortars, Plasters, and Stuccos: The Puuc Area

AbstractChemical and microscopic examination of building materials from Uxmal, Kabah, Sayil, and Labná demonstrate the presence of all the building elements previously identified at Comalcalco, Las Flores, and Palenque: mortar, plaster, stucco, wash coat, and lime-aggregate. The building elements at these Puuc sites differ from those at Comalcalco and Las Flores in the use of non-marine sources of lime, greater strength, and generally smoother composition. They differ from the Palenque building elements in the lack of multi-laminate structure and the absence of very smooth and highly worked outer surfaces. It is possible that some form of lime other than that obtained by burning limestone was used. An inclusion of gypsum found at Uxmal is the only such component identified at any of the Mesoamerican sites studied so far.