Amount Of Free Lime Research Articles

Effect of weather aging on volume expansion properties of steel slag


 
 
 
 Steel slag, one of the huge industrial waste sources, which has many outstanding advantages (hardness, roughness, angularity, and abrasion resistance) has been used as an aggregate in asphalt concrete to bring many benefits. However, steel slag is rarely used in Portland cement concrete because of concerns that it may give rise to volume expansion. One of the main causes of this problem is that the steel slag contains a considerable amount of free lime. This free lime content can be reduced if it is hydrated or the steel slag is aged by water. Therefore, in this study, the effects of weather aging on volume expansion properties of steel slag will be considered. The pH, free lime and volume expansion tests were carried out on weather-aged steel slag samples (after aged by 1 month, 6 months, 12 months and 30 months) and compared with non-aged one. The results showed that the 6 month-aged, 12 month-aged, and 30 month-aged steel slag samples had low free content, low pH and volume expansion. Moreover, steel slag aged more than 6 months has very low volume expansion, meeting the requirements of ASTM D492 for use as aggregate in concrete.
 
 
 

Effect of weather aging on volume expansion properties of steel slag


 
 
 
 Steel slag, one of the huge industrial waste sources, which has many outstanding advantages (hardness, roughness, angularity, and abrasion resistance) has been used as an aggregate in asphalt concrete to bring many benefits. However, steel slag is rarely used in Portland cement concrete because of concerns that it may give rise to volume expansion. One of the main causes of this problem is that the steel slag contains a considerable amount of free lime. This free lime content can be reduced if it is hydrated or the steel slag is aged by water. Therefore, in this study, the effects of weather aging on volume expansion properties of steel slag will be considered. The pH, free lime and volume expansion tests were carried out on weather-aged steel slag samples (after aged by 1 month, 6 months, 12 months and 30 months) and compared with non-aged one. The results showed that the 6 month-aged, 12 month-aged, and 30 month-aged steel slag samples had low free content, low pH and volume expansion. Moreover, steel slag aged more than 6 months has very low volume expansion, meeting the requirements of ASTM D492 for use as aggregate in concrete.
 
 
 

Effect of weather aging on volume expansion properties of steel slag


 
 
 
 Steel slag, one of the huge industrial waste sources, which has many outstanding advantages (hardness, roughness, angularity, and abrasion resistance) has been used as an aggregate in asphalt concrete to bring many benefits. However, steel slag is rarely used in Portland cement concrete because of concerns that it may give rise to volume expansion. One of the main causes of this problem is that the steel slag contains a considerable amount of free lime. This free lime content can be reduced if it is hydrated or the steel slag is aged by water. Therefore, in this study, the effects of weather aging on volume expansion properties of steel slag will be considered. The pH, free lime and volume expansion tests were carried out on weather-aged steel slag samples (after aged by 1 month, 6 months, 12 months and 30 months) and compared with non-aged one. The results showed that the 6 month-aged, 12 month-aged, and 30 month-aged steel slag samples had low free content, low pH and volume expansion. Moreover, steel slag aged more than 6 months has very low volume expansion, meeting the requirements of ASTM D492 for use as aggregate in concrete.
 
 
 

Lightweight masonry block without Portland cement

ABSTRACT Huge amounts of fly ash - a substance that does not conform to the ASTM C618 classification due to its chemical properties - have been abandoned in landfills around the world, despite their self-cementing property. It has not been used in concrete making applications due to its large amounts of free lime and sulfate contents. The fly ash in these plants is dumped in landfills, causing serious environmental hazards. Fly ash is disposed to the landfills by belt conveyors after being humidified with water. Therefore, the fly ashes humidified in the landfill areas are hydrated in nature. This hydration is further intensified in landfills by rain and snow. Thus, the free lime content of fly ash decreases due to its long hydration process. In this work, the lightweight masonry blocks were produced by mixing normal and hydrated fly ashes or normal, hydrated fly ash and lime without Portland cement. The compressive strength, water absorption, sorptivity, density, porosity, and thermal conductivity values of the samples produced were determined. The results obtained from these tests showed that lightweight masonry blocks could be produced by using these waste materials in building applications.

Utilization of high-calcium fly ashes through mineral carbonation: The cases for Greece, Poland and Spain

Limited utilization possibilities of high–calcium fly ashes (HCFA) are a serious issue not only in Europe, but also worldwide. The properties of such waste from coal-fired power plants could be conveniently treated in order to make their compositions compliant with national regulations and allow their use in a variety of industrial applications. This work reports on an investigation of mineral carbonation of HCFA from Greece, Poland and Spain with total CaO contents between 10 and 15 wt.%. Two types of experiments, batch and continuous flow, with and without the addition of water vapor, were performed. Best carbonation efficiency obtained was 47% of the bulk CaO content. The free lime content of the samples was found to be the controlling factor. After treatment, the amount of free lime was reduced to values suitable for their utilization as supplementary cementitious materials. The addition of water to the system played also an important role in the progress of the carbonation reactions. Our results strongly suggest that a carbonation treatment of HCFA could contribute to the circular economy of such waste materials and potentially increase their utilization in the construction industry, as well as make a significant contribution to lowering of the CO2 emissions in coal-burning industrial facilities.

Effect of basic oxygen furnace slag type on carbon dioxide sequestration from landfill gas emissions

This study investigates the carbon dioxide (CO2) sequestration potential of three different basic oxygen furnace (BOF) slags (IHE-3/15, IHE-9/17, and Riverdale) subjected to simulated landfill gas (LFG) conditions (50% CH4 and 50% CO2 v/v) in a series of batch and column experiments. Batch experiments were performed at different moisture contents (0%, 10%, 15% and 20% moisture by weight) and temperatures (7 °C, 23 °C and 54 °C) to examine the effect of moisture and temperature on the CO2 sequestration potential of the BOF slags. The column experiments were conducted under continuous humid gas flow conditions. The results from the batch experiments show that the CO2 sequestration was significantly higher in a moist state (10%, 15%, 20% moisture (w/w)) versus the dry state (0% moisture). The optimum moisture content (w/w) for CO2 sequestration was different for each BOF slag; IHE-3/15 (10%), IHE-9/17 (20%) and Riverdale (20%). The variation in ambient temperature did not show any significant effect on the CO2 sequestration capacity of the BOF slags. The CO2 sequestration capacity of IHE-3/15, IHE-9/17 and Riverdale BOF slags determined by long-term batch experiments were 105 mg/g, 80 mg/g and 67 mg/g, respectively. The IHE-3/15 slag demonstrated the highest carbonation potential and was attributed to its finer particle size and higher free lime, portlandite and larnite content. The IHE-9/17 and Riverdale slags showed significantly lower CO2 sequestration capacity in comparison to the IHE-3/15 slag. The amount of free lime, portlandite and larnite, which are considered to be the most reactive minerals during carbonation, was nearly 1.3 times less than that of the IHE-3/15 slag in the IHE-9/17 and Riverdale slags. Also, the Riverdale slag showed relatively lower CO2 sequestration in column experiment in comparison to the batch experiments, perhaps due to a high in-situ density which limited CO2 diffusion and hence the CO2 uptake. Overall, this study provides a means to analyze the suitability of the use of BOF slags in landfill covers for mitigating fugitive CO2 emissions from landfills.

Use of wood dust fly ash from an industrial pulverized fuel facility for rendering

Wood dust II fly ash, which was generated after boiler retrofit (implementation of low-NOx burners combined with over-fire air), apparently is an enhanced quality for rendering. This is attributed to the mineral phases formed, an increase in the amount of free lime, and performance test results. After accelerated aging tests, the wood dust II fly ash showed no visible occurrence of cracks or detachment of the render base coat from the substrate. Tensile strength values met the applicable limit requirement of 8 MPa. The results contribute to a sustainable ash management for wood fly ash from pulverized fuel facilities.

Monitoring the free lime content in lime mud using zeta potential

The presence of unreacted lime (free lime) in the lime mud can cause many problems in the chemical recovery operation of kraft pulp mills. There are currently no standards for free lime determination. Conventional methods used in mill laboratories require extensive preparations and give inconsistent and sometime erroneous results. A systematic study was performed to determine if zeta potential, a dispersion characteristic of the lime mud and liquor slurry, can be used to indirectly indicate the amount of free lime in the lime mud. Lime mud with different free lime contents was produced in the laboratory by causticizing green liquors with lime at different liming ratios. The results show that zeta potential changes from negative to positive when the free lime in lime mud exceeds a critical value. This unique characteristic enables a rapid detection of free lime.

The impact of natural ornamental limestone dust on swelling characteristics of high expansive soils

Expansive soils are considered as a potential natural hazard if they are not adequately treated. Expansive soils have high potential for shrinking and swelling under changing moisture conditions and cause extensive damages to engineering infrastructures. This study is concerned with the suitability of natural ornamental limestone dust to reduce the swelling characteristics of high expansive soils. The results are revealed that the swelling pressure and percent of heave are greatly decreased with increasing the inserted core diameters and mixing percentages of limestone dust. The average reduction percent values of swelling pressure and percent of heave are increased from 2.21% to 43.09% and from 2.56% to 45.64%, respectively, for treated soil samples with increase in limestone dust core diameters from 5 mm to 20 mm (1% to 16% of total soil area). The average reduction percent values of swelling pressure and heave percent are increased from 10.29% to 70.73% and from 22.29% to 82.90%, respectively, for treated soil samples with increase in limestone dust mixing percentages from 10% to 30%. The results are revealed that the enhancement in swelling characteristics of high expansive soils that are treated by ornamental limestone dust is mostly attributed to the replacement of high expansive fine clay particles by non-expansive and non-plastic coarse limestone dust particles, and to the presence of a considerable amount of free lime in limestone dust (4.97% as [Ca(OH)2]) that is responsible for converting the high expansive soils to less expansive soils by pozzolanic reaction. The mixing treatment method is more suitable for surficial and shallow foundation high expansive soil beds, while the compacted limestone dust piles “inserted limestone dust core method” are more suitable for deep foundation high expansive soil beds.

The Influence of Barium Sulphate and Barium Carbonate on the Portland Cement

Shielding of different types of radiation should be studied these days when there is a great development in the field of nuclear science. Barium ions can shield different type of radiation, therefore, by incorporation of barium ions into the system of Portland clinker, a binder with shielding properties can be made. The work is focused on influence of barium ions on the formation of Portland clinker and its properties. As a source of barium, barium sulphate and barium carbonate were added to raw meal. Clinkers and cements with a different amount of barium were prepared and the effect of barium on the clinker and cement properties respectively was studied. By Rietveld analysis (using X-Ray diffraction) and microscopic point counting method, the ratio of clinker phases was studied. With increasing amount of barium, the alite: belite ratio was decreasing and the amount of free lime was increasing. Sulphate decelerates the decreasing ratio and causes grow of alite crystals to great dimensions. The presence of barium in different phases was observed by SEM with EDS. The highest amount of barium was found in belite and clinker melt. In clinker melt, conglomerations of barium were formed. Furthermore, a difference in formation temperature of clinker phases was observed and some elementary tests were done on prepared cements according to the European standards.

Quantitative Determination of Free Lime Amount in Steelmaking Slag by X-ray Diffraction

Steelmaking slag is a by-product of steel making. It has been reused as a material for civil engineering, pavement construction etc. For such applications, it is extremely important to evaluate the amount of free lime, which has the chemical form of calcium monoxide (CaO) and can cause the failure of mechanical properties by volume expansion through absorption of water or carbon dioxide gas. So far, various chemical analyses of the free lime content have been employed that are frequently combined with ethylene glycol extraction. Unfortunately the method does not always distinguish the chemical form of calcium. In the present paper, we propose the use of X-ray diffraction. The technique can clearly show the existence of different chemical forms of calcium, such as CaO, Ca(OH)2, CaCO3, and calcium silicates such as Ca2SiO4 and other forms as different peaks. As the technique is non-destructive, one can also use other chemical analyses for the same samples. The amount of free lime can be determined by the standard addition method. In our study, the content of free lime in slag powder of under 32 micron dia was determined as 11.5 mass%. It was also found that the amount of free lime can be effectively decreased to 3–5 mass% by hot steam and/or carbonation processes.

Effects of Pair-Mineralizer on Burnability of Clinker and Formation of Mineral

The effects of the pair-minerializer (CaSO4,-CaF2) on the burnability of clinker and the formation of mineral are investigated. As experimental results, the addition of F as pair-mineralizer, the burnability of clinker was improved. Especially, the addition of F and SO3 components simultaneously as pair-mineralizer, total amount of free lime in clinker is rapidly decreased compared with the value which mineralizer was added separately. In case of adding K2O only to the raw mixes, the amount of free lime is increased. However, if alkali (K2O) and pair-minerializer (CaSO4,-CaF2) were added simultaneously, the produced amount of clinker mineral is increased due to the formation of stable calcium langbeinite by the combination of alkali (K2O) and sulfate

Effect of CaF 2 and MgO on sintering of cement clinker

CaF 2 (0.25, 0.50, and 1%) and MgO (1, 2, and 3%) was added to a mixture composed from limestone, sand, and loam, then burned at 1410°C for 112 min. Clinker samples were cooled to room temperature and the amount of free lime (CaO f) was determined by titration while the relative amounts of alite and belite were determined by X-ray diffraction (XRD). Microstructure was investigated by scanning electron microscopy (SEM). The amount of alite decreased in CaF 2-added samples and the amount of belite increased. The CaO f content of the sample containing 1% MgO was less than that of the pure sample. For the other MgO-added samples, due to the increase in lime saturation factor value no evident change was detected in the amount of CaO f. Both XRD and SEM analyses showed a decrease of the amount of alite and an increase of the amount of belite in MgO-added samples when compared to pure samples. The reason for the decrease in amount of alite in MgO-added samples is believed to be coarse belite crystals. Due to the prolonged holding time at the alite formation temperature, coarse belite crystals were formed. Because of the high diffusion rate at this period, belite crystals lose their surface activity and consequently alite formation was hindered.

Origin and characterisation of fly ashes from cellulose industries containing high proportions of free lime and anhydrite

Fly ashes from cellulose industries originate from different internal waste combustion processes. Because they contain considerable amounts of free lime and anhydrite, they are potential secondary raw materials for the production of building products. The source of the CaO is a Ca-bisulphite-sludge originating from the cellulose extraction process. The CaO/anhydrite ratio in this lime-sulphate fly ash depends on the extent of sulphur reduction by organic carbon during the combustion process. A second type of Al-bearing ash contains additionally lowly reactive calcium silicates and highly reactive calcium aluminate phases originating from combusted paper sludge containing kaolinite. Both ashes show a reduced reactivity compared to commercial lime as it is used for the production of autoclaved aerated concrete. The reduced activity is related to the coated surfaces of the CaO and elevated sulphate and alkali contents.

Fly ash from cellulose industry as secondary raw material in autoclaved aerated concrete

Because fly ash from cellulose industries contains considerable amounts of free lime and sulfate, they are potential secondary raw materials for the production of autoclaved aerated concrete. Laboratory experiments were performed by replacing lime and sulfate in conventional autoclaved aerated concrete mixtures by fly ash. Compared to a reference series, samples with even higher compressive strength could be produced with lime-sulfate ash. At higher proportions of fly ash, the formation of calcium silicate hydrate phases is delayed and the presence of unreacted portlandite and newly formed scawtite produce a drop in strength and an increase in shrinkage. Low strength resulted by using Al-bearing ash with a lower amount of free CaO, which makes this type of ash not applicable in practice.

X.R.F Analysis of Steelmaking Slags Using Special Sample Preparation Techniques

X.R.F. analysis of steelmaking slags has been done routinely since the 1960s. Fused buttons or pressed powdered pellets are used.Under certain conditions steelmaking slags may contain appreciable amounts of free lime and metallic iron droplets. These can cause gross inaccuracies in the result of the X.R.F. analysis as the normal correction procedures used in X-ray fluorescence techniques can not compensate for them.A special sample preparation technique as well as appropriate analytical procedures will be discussed. Examples of slags with different levels of free lime and metallic iron will be shown.

CHS(I) — Binder of potentially superior strength

Because fly ash from cellulose industries contains considerable amounts of free lime and sulfate, they are potential secondary raw materials for the production of autoclaved aerated concrete. Laboratory experiments were performed by replacing lime and sulfate in conventional autoclaved aerated concrete mixtures by fly ash. Compared to a reference series, samples with even higher compressive strength could be produced with lime-sulfate ash. At higher proportions of fly ash, the formation of calcium silicate hydrate phases is delayed and the presence of unreacted portlandite and newly formed scawtite produce a drop in strength and an increase in shrinkage. Low strength resulted by using Al-bearing ash with a lower amount of free CaO, which makes this type of ash not applicable in practice.

STUDIES ON MIXED PORTLAND CEMENTS, XVIII

The author reported, in continuing the previous studies (This Journal, 1933, 41, 623; 1934, 42, 273, 628, 688; 1935, 43, 215, 572; 1936, 44, 22, 617; 1937, 45, 8), the results of further studies on mixed Portland cements. The report of the present paper is the continued tests of high silica mixed Portland cements, which were already studied on their common physical properties and chemical compositions. The brief summary is abstracted from the original Japanese paper, as following:(1) The paste of neat cement was kneaded with the amount of water of normal consistency for determining the time of setting, and moulded to small cylindrical test pieces (Dia.: 5cm and Ht.: 10cm). These test pieces were cured in four serie-(a) in water for 7 days, (b) in water for 28 days, (c) in water for 7 days and then in warm (50°C) water for 7 days, and (d) in water 7 days and then in warm (50°C) water for 28 days. The compressive strengths of these four series of cured specimens, were tested and the hardened samples were quickly taken from the fresh part of the crushed pieces after strength tests and dried in desiccator. The chemical compositions were determined and the amounts of free lime or hydrated lime were specially determined and compared for these four series of curing (a), (b), (c) and (d), which are tabulated in the table 1.Table 1 Amounts of Free Lime in Hardened CementsFrom these results, it can be clearly observed that the amount of free calcium hydroxide increses in Portland cement and on the contrary decreases in mixed Portland cement. This fact shows that the high siliceous admixture used in mixed Portland cement combines with calcium hydroxide set free by the hydration, which owes to clinker part 60-75% of cement.(3) The strengths of dry (or non-plastic) and wet (or plastic) mortars of these cements were tested in the longer curing ages (3, 6 and 12 months) than the standard curing ages 3, 7 and 28 days, which strengths were already reported in the foregoing report (This Journal, 1937, 45, 8). The increase of strength is greater in high silica mixed Portland cements than in the common Portland cements, which owes to the same reason with the combination of siliceous admixture and calcium hydroxide produced in set cement.(4) The expansion or contraction of mortars were tested by the prismatic (4×4×16cm) test pieces moulded by wet mortars and cured in water for 3, 7, 28, 91 (3 months), 182 (9 months) and 364 (12 months) days. The results show the fact that the contraction or expansion was not greater in the case of high silica mixed Portland cement than in the case of common Portland cement, which is quite contrary in air curing.(5) The corrosion, expansion or contraction, and decrease or increase of strength by curing in water, 10% NaCI solution and 10% Na2SO4 solutions were fully studied by using the prismatic test pieces of wet mortar, which were vertically dipped in water or salt solutions for 4, 8, 12, 16, 20 and 24 weeks. The expansion crack and then disintegration were seen in the test pieces dipped in 10% Na2SO4 solution and especially considerable in common Portland cement and blast furnace slag cement. This result owes to the large amount of alumina in the cement, and the formation of xCaO⋅yAl2O3⋅zCaSO4⋅nH2O (so-called cement bacillus). This results were clearly shown by the photographs of the disintegrated test pieces, and coincide quite well with those recently reported by G. Haegermann (Zement, 1937, 26, 210).(6) The strengths were tested b these corroded test pieces after expansion test for 24 weeks curing above described. The decrease of strength was most remarkable in the specimens cured in 10% Na2SO4 solution, and then followed by those cured in water and 10% NaCl

Studies on Setting Free of Lime from Cement, Clinker and Its Hydraulic Compounds by Heating

The setting free of lime from cement by reheating is a very interesting problem with regrrds to the cement chemistry. There are many reports in these years with regards to this problem, e. g., S. L. Meyers, Rock Products, 1930, 33, No. 8, 78; E. T. Carlson, Rock Products, 1931, 34, No. 25, 52; G. E. Bessy, Cement and Cement Manufacture, 1932, 5, 233; D. Steiner and B. Bartos, Tonind. =Ztg., 1932, 56, 1040; G. Ashkenasi, Tonind. =Ztg., 1932, 56, 1065. But it is very sorry that the earliest study about this problem by Prof. Haruhiko Cho (The Journal of the Society of Chemical Industry, Japan, 1929, 32, 57C; Technical News of the Kyushu Imperial University, Japan) was not introduced and paied attention by the European and American cement chemists, owing to the want of foreign abstract to this paper.In the present paper, it is principally reported the results of studies on the source of setting free of lime by reheating cement, clinker, and various hydeaulic compounds, i.e., calcium silicates and calcium aluminates. The brief summary from the original Japanese paper is as follows:(1) The setting free of lime by reheating cement does not be made clear only by the decomposition of tricalcium silicate to dicalcium silicate and lime, i.e., 3CaOSiO2→2CaO SiO2+CaO.(2) This decomposition of 3CaOSiO2 to 2CaO2 SiO and CaO is clearly accelerated by mixing gypsum, dicalcium ferrite (2CaO·Fe2O3), calcium fluoride (CaF2), etc., but not by the presence of calcium phosphate [Ca3(PO4)2], dicalcium silicate (2CaOSiO2), tricalcium aluminate (3CaOAl2O3), magnesia, etc.(3) Tricalcium aluminate, dicalcium silicate and dicalcium ferrite do not set free lime by heating But tricalcium aluminate sets free lime only by the presence of gypsum.(4) From these results, it will be recognized that the main part of free lime produced by heating clinker is due to the decomposition of tricalcium silicate by the presence of dicalcium ferrite and the amount of free lime by this decomposition is not so much, owing to the weaker effect of dicalcium ferrite than that of gypsum.But the decomposition of free lime by heating cement is very considerable. This is mainly due to the presence of gypsum, which has the strong effect to the decomposition of tricalcium silicate to dicalcium silicate and lime by heating about at 1050-1150°C. Sometimes the amount of free lime becomes greater than that of one molecule of lime from tricalcium silicate, i.e., 3CaOSiO2→2CaOSiO2+CaO. This excess of lime clearly comes from the decomposition of tricalcium aluminate by the prerence of gypsum, which is easily explained by the result above cited (3). So that, the amount of free lime produced by heating cement (the ground product from the clinker with gypsum) is the total sum of the lime from (1) the decomposition of tricalcium silicate by the effects of gypsum and dicalcium ferrite, and (2) the decomposition of tricalcium aluminate by the effect of gypsum.Further studies on this problem will be continued and reported hereafter by the present authors.

The Amount of Free Lime and the Composition of the Soluble Phosphates in Basic Slag

Basic Slag owes its value as a source of phosphoric acid to the fact that it is essentially basic in its character, and can be used on land where an acid manure of the character of superphosphate is not to be recommended.As no figures were available on the subject it seemed interesting to determine how much of the lime which it contains existed in the free uncombined condition. It has been stated that in some cases this is as much as 20%.With a view to this determination four samples of freshly ground slag were obtained direct from the makers through the kindness of the Lawes Chemical Manure Company.