• The Journal of Engineering Geology
• /
• v.12 no.1
• /
• pp.95-109
• /
• 2002

A significant question is what role does newly-formed expansive mineral growth play in the premature deterioration of concrete. These minerals formed in cement paste as a result of chemical reactions involving cement paste and coarse/fine aggregate. Petrographic observations and SEM/EDAX analysis were conducted in order to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from lowa concrete highways that showed premature deterioration. Formation and expansive mechanisms involved in deterioration were Investigated. Brucite, Mg(OH)$_2$, is potentially expansive mineral that farms in cement paste of concretes containing reactive dolomite aggregate as a result of partial dedolomitization of the aggregate. No cracking was observed to be spatially associated with brucite, but most brucite was microscopic in size and widely disseminated in the cement paste of less durable concretes. Expansion stresses associated with its growth at innumerable microlocations may be retrieved by cracking at weaker locations in the concrete. Ettringite, 3CaO.Al$_2$O$_3$.3CaSO$_4$.32$H_2O$, completely fills many small voids and occurs as rims lining the margin of larger voids. Microscopic ettringite is common disseminated throughout the paste in many samples. Severe cracking of cement paste causing premature deterioration is often closely associated with ettringite locations, and strongly suggests that ettringite contributed to deterioration. Pyrite, FeS2, is commonly present in coarse/fine aggregates, and its oxidation products is observed in many concrete samples. Pyrite oxidation provides sulfate ions for ettringite formation.

• Journal of the Korea Concrete Institute
• /
• v.29 no.4
• /
• pp.415-424
• /
• 2017

The purpose of this study is to investigate the effect of sulfate (${SO_4}^{2-}$) and magnesium ($Mg^{2+}$) ions on sulfate resistance of Alkali-activated materials using Fly ash and Ground granulated blast furnace slag (GGBFS). In this research, 30%, 50% and 100% of GGBFS was replaced by sodium silicate modules ($Ms(SiO_2/Na_2O)$, molar ratio, 1.0, 1.5 and 2.0). In order to investigate the effects of $Mg^{2+}$ and ${SO_4}^{2-}$, compression strength, weight change, lengh expansion of the samples were measured in 10% sodium sulfate ($Na_2SO_4$), 10%, 5% and 2.5% magnesium sulfate ($MgSO_4$), 10% magnesium nitrate ($Mg(NO_3)_2$), 10% [magnesium chloride ($MgCl_2$) + sodium sulfate ($Na_2SO_4$)] and 10% [magnesium nitrate $(Mg(NO_3)_2$ + sodium sulfate ($Na_2SO_4$)] solution, respectively and X-ray diffraction analysis was conducted after each experiment. As a result, when $Mg^{2+}$ and ${SO_4}^{2-}$ coexist, degradation of compressive strength and expansion of the sample were caused by sulfate erosion. It was found that the reaction of $Mg^{2+}$ with Calcium Silicate Hydrate (C-S-H) occurred and $Ca^{2+}$ was produced. Then the Gypsum ($CaSO_4{\cdot}2H_2O$) was formed due to reaction between $Ca^{2+}$ and ${SO_4}^{2-}$, and also Magnesium hydroxide ($Mg(OH)_2$, Brucite) was produced by the reaction between $Mg^{2+}$ and $OH^-$.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2014.11a
• /
• pp.23-24
• /
• 2014

Currently, cement and concrete industries have been contributing to the CO₂ emission worldwide. Because of that, the efforts to minimize CO₂ have been the subject of many researches. This study focus on the use of GGBFS and fly ash in mortar specimens as a patial replacement of cement. Because of the limitation of the initial compressive strength, the newly efforts to enhance the strength through CO₂ Curing was adapted. To accelerate the reaction with CO₂, MgO was replaced by percentage from 0 to 100%. Results showed that compressive strength values at 7 days with CO₂ curing done on specimens was higher than that with no CO₂ curing. Similar trend was observed at 14 days too. It is therefore appeared that CO₂ curing has an obvious effect on compressive strength development of mortar specimens.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.87-88
• /
• 2022

The use of converter slag as an aggregate for concrete is limited due to the risk of expansion. This study analyzed the substances causing the expansion of converter slag and evaluated the possibility of its use as an aggregate for concrete through separation and selection. As a result of the experiment, it was confirmed that CaO and MgO were concentrated in the slag particles inducing expansion, and it was confirmed that it was possible to separate them from non-expanded particles through magnetic.

• Advances in concrete construction
• /
• v.9 no.3
• /
• pp.267-278
• /
• 2020

This paper reports on the result of an experimental investigation carried out to study the compressive strength and sorptivity properties of blended cement concrete exposed to 5% and 10% MgSO₄ solution using fly ash (FA) and silpozz. Usually in sulphate environment the minimum grade of concrete is M30 and the mix design is done for target mean strength of 39 MPa. Silpozz is manufactured by burning of agro-waste rice husk in designed furnace in between 600° to 700℃ which is one of the main agricultural residues obtained from the outer covering of rice grains during the milling process. There are four mix series taken with control mix. The control mix made 0% replacement of FA and silpozz with Ordinary Portland Cement (OPC). The first mix series made 0% FA and 10-30% replacement of silpozz with OPC. The second mix series made with 10% FA and 10-40% replacement of silpozz with OPC. The third mix series made 20% FA and 10-30% replacement of silpozz with OPC and the fourth mix series made 30% FA and 10-20% silpozz replaced with OPC. The samples (cubes) are prepared and cured in normal water and 5% and 10% MgSO₄ solution for 7, 28 and 90 days. The studied parameters are compressive strength and strength deterioration factor (SDF) for 7, 28 and 90 days. The water absorption and sorptivity tests have been done after 28 days of normal water and magnesium sulphate solution curing. The investigation reflects that the blended cement concrete incorporating FA and silpozz showing better resistance against MgSO₄ solution when compared to normal water curing (NWC) samples.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.4
• /
• pp.310-315
• /
• 2019

This study conducted a series of studies to find alternative ways to use Chlorine Bypass System-dust(CBS-dust) in cement production. The results of engineering characteristics of CBS-dust are summarized as follows. First of all, the density of CBS-dust is 2.40, lighter than cement and the pH was 12.50 which was strong alkaline. In terms of particle size, it was 11.70 ㎛ which was finer than cement. With chemical properties, calcium oxide(CaO) was the highest as 35.10%, potassium oxide(K₂O) was 32.43%, potassium chloride(KCl) was 19.46%, sulfur oxide(SO₃) was 6.81%, and the remaining chemical components are SiO₂, Fe₂O₃, Al₂O₃, MgO, and the like. Therefore, if CBS-dust is used as early-strength chemical admixtures in the concrete secondary products that use a large amount of mineral admixtures without rebar, it can be an effective method for increasing the strength of concrete as an alkali activator and preventing early-frost damage of Cold Weather Concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.533-536
• /
• 2008

This study is the application of phosphate magnesia cement for solidification of soils. The object of the study is the application of the pavment of the farm roads. The new pavement method must be environmental, ecologic and durable. So, for solidification of farm road's soil, we use magnesia cement as quick setting, high strength materials. At magnesia phosphate cement, mixing ratio of mono ammonium phosphate and magnesia is 4:6 and w/b is 50 wt%, it show 14 MPa of compressive strength, and high hydration heat. Solidified soils that mixing ratios of magnesia cement and soil are 4:6 and 5:5 have very high durability for freezing and thawing.

• Economic and Environmental Geology
• /
• v.36 no.5
• /
• pp.365-374
• /
• 2003

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, $MgCl_2$ and $Na_2SO_4$ solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({$Ca_6/[Si(OH)_6]_2{\cdot}24H_2O$}${\cdot}[(SO_4)_2]{\cdot}[(CO_3))2]$) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).

• Journal of the Korea Concrete Institute
• /
• v.23 no.2
• /
• pp.195-201
• /
• 2011

This paper estimates the structural performance of spirally confined concrete having electric arc furnace (EAF) oxidizing slag aggregates. The EAF oxidizing slag is a by-product generated from iron and steel industry. The EAF oxidizing slag have been largely put to low-value-added uses due to its expansive properties of the free-CaO and free-MgO. Recently, this problem has been solved by the advances in steelmaking technology and thereby stabilizing EAF oxidizing slag aggregate. To verify the application of the EAF oxidizing slag aggregate to the structural concrete usage, a total of 27 cylindrical specimens with a diameter of 150 mm and a height of 300 mm were cast and tested. The test parameters were aggregate type and spiral reinforcement yield strength. Experimental results showed that the structural performance of specimens with EAF oxidizing slag aggregates was equivalent to that of confined concrete with natural aggregates.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.3
• /
• pp.185-194
• /
• 2022

Coffee is one of the most consumed beverages in the world and is the second largest traded commodity after petroleum. Due to the great demand of this product, large amounts of waste is generated in the coffee industry, which are toxic and represent serious environmental problems. This study aims to study the possibility of recycling spent coffee grounds (SCG) as a mineral admixture by replacing the cement in the manufacturing of concrete. To recycle the coffee g rounds, the SCG was dried to remove moisture and fired in a kiln at 850 ℃ for 8 hours. Carbonized coffee grounds are produced as coffee grounds ash (CGA) through ball mill grinding. The chemical composition of the prepared coffee grounds ash was investigated using X-ray fluorescence (XFR). According to the chemical composition analysis, the major elements of coffee grounds ash are K₂O(51.74 %), CaO(15.92 %), P₂O₅(14.39 %), MgO(7.74 %) and SO₃(6.89 %), with small amounts of F₂O₃(0.66 %), SiO₂(0.59 %) and Al₂O₃(0.31 %) content. To evaluate quality and mechanical properties, substitutions of 5, 10, and 15 wt.% of coffee grounds ash (CGA) were tested. From the quality test results, the 28-day activity index of CGA5 reached 80 %, and the flow value ratio reached 96 %, which is comparable to the minimum requirement for second-grade FA. From the test results of the mortar, the optimal results have been found in specimens with 5 wt-% coffee grounds ash, showing good mechanical and physical properties.