Silicate Admixture Research Articles

PROPERTIES OF CONCRETE MODIFIED BY AMORPHOUS ALUMINA SILICATE

Concrete is the most widely used building material obtained by hardening the mix made of coarse and fine aggregates, cement as the binding material, and water. The basic properties of concrete depend on the quality and properties of cement, w/c ratio and the homogeneity of compaction. Compressive strength is one of the most important properties of concrete. Materials used: Portland cement CEM I 42.5 R, 0/4 fraction sand, 4/16 fraction gravel, amorphous alumina silicate admixture, polycarboxylate ether-based superplasticizer Muraplast FK 63.30, and tap water. Five compositions of concrete mixes containing 0%, 2.5%, 5%, 7.5% and 10% of amorphous alumina silicate admixture by mass of cement were produced. The article analyses the effect of amorphous alumina silicate on the properties of concrete depending on the admixture content. The results revealed that the compressive strength of concrete after 7 days of curing increased by 7.1%, after 28 days of curing increased by 13.3% when the amorphous aluminum oxide doped silicate content was increased to 10%. Amorphous alumina silicate admixture added in quantities of up to 10%, increased the density of hardened concrete by 0.75%, and ultrasonic pulse velocity in specimens with the admixture increased up to 2.63%.

Microstructure Changes in Hardened Cement Paste after Freezing – Thawing Cycles

This article analyses the results of the freezing – thawing with deicing salt test where changes in the microstructure of the surface layer in contact with aggressive environment of hardened cement paste produced with and without sodium silicate (hereinafter NTS) admixture were observed after freeze-thaw cycles in the presence of calcium chloride. After 56 cycles of freezing – thawing with deicing salt test micro-cracks and cavities were observed in the microstructure of the surface layer of hardened cement paste with and without NTS admixture. In the case of hardened cement paste with NTS admixture changes in the microstructure of the surface layer are less prominent: the number and size of cavities and micro-cracks are smaller. The test revealed that compressive stress, which before freezing – thawing with deicing salt test was very similar in hardened cement paste with and without NTS admixture (85.4 MPa and 82.8 MPa respectively), changed after 56 cycles of freezing – thawing with deicing salt test as follows: reduced by 39.5 % in concrete without NTS admixture and increased slightly (2.5 %) in hardened cement paste with NTS admixture. Based on the test results the authors arrived at the conclusion that sodium silicate solution can be effectively used to extend the useful life of hardened cement paste exposed to freeze-thaw cycles and affected by CaCl 2 . DOI: http://dx.doi.org/10.5755/j01.ms.19.1.3835

Microstructure and Mechanism of Concrete Using Inorganic Silicate Admixture

The study evaluates the properties of concrete mixed with inorganic silicate admixture. The admixture was used in proportions of 3%, 5%, and 7% of the weight of the cement. We performed tests on compressive strength and elastic modulus to evaluate the mechanical properties of concrete. Results show that the addition of the inorganic silicate admixture has a positive influence on the mechanical properties of concrete, with the best results obtained with 3% admixture. MIP porosity measurements determined that the addition of inorganic silicate admixture increased the density of the porous structure. SEM microscopic analysis revealed many needle-like protrusions into the porous structure of concrete. XRF chemical composition analysis indicated that these structures comprised mainly Na2O and SiO2. Can with cement hydration products Ca(OH)2 bring in Chemical reaction. Inferred pore structure Within be C-S-H gel of needle-like protruding structure. it can improve the main cause of mechanical properties of concrete.

Experimental study of liquid immiscibility in the fluid-magmatic silicate systems containing Ti, Nb, Sr, REE, and Zr

Aluminosilicate alkaline systems containing Ti, REE (La, Ce), Y, Sr, and Nb were studied experimentally at T = 1200 and 1250°C and P = 2 kbar in the presence of aqueous and alkaline fluid. In the fluid-absent experiments with systems containing the same elements, loparite crystals in a silicate matrix were obtained. These systems in the presence of aqueous and alkaline fluid pressure conditions demonstrate an immiscible splitting into two liquids: (1) aluminosilicate matrix and (2) droplets enriched in Ti, REE (La, Ce), Y, Sr, and Nb, which contain silicate admixture and are compositionally close to loparites. According to approximate estimates, the partition coefficients between the melts of the droplets and aluminosilicate matrix (K = C dr/C sil) are more than 5 for TiO2, 15 for REE, and from 2.3 to 7.6 for SrO. Obtained unmixing may be of great significance for explaining the genesis of REE-Nb (loparite) deposits. In addition, the experiments demonstrate that Zr may be accumulated together with Ti and REE due to liquid immiscibility of this type. The partition coefficient of ZrO2 between the melts of droplets and aluminosilicate matrix (K = C dr/C sil) according to approximate estimates varies from ∼ 3.5 to 9.

Alkali–silica reaction, pessimum effects and pozzolanic effect

The pessimum proportion and pessimum size effects for alkali–silica reaction-induced deterioration of concrete (ASR) and the pozzolanic effect of fine siliceous admixtures in concrete have been explained based on the proposed ASR model [T. Ichikawa, M. Miura, Modified model of alkali–silica reaction, Cem. Concr. Res. 37 (2007) 1291–1297.]. The attack of alkali hydroxide to aggregate particles composed of ASR-reactive minerals generates the layer of hydrated mature alkali silicate and the layer of less hydrated immature alkali silicate under the mature layer. The mature alkali silicate preferentially reacts with Ca 2+ ions to convert to fragmental calcium alkali silicate, because the reaction accompanies a significant volume contraction. The immature alkali silicate gradually reacts with Ca 2+ ions to cover the surface of the reactive minerals with tight layers of calcium alkali silicate called reaction rims. The reaction rims allow the penetration of alkaline solution but prevents the leakage of viscous alkali silicate generated afterward, so that the alkali silicate is accumulated inside the rims to give an expansive pressure enough for cracking the aggregate and the surrounding concrete. Due to the absorption of Ca 2+ ions by mature alkali silicate, too much increase of the proportion of reactive aggregate causes the deficiency of Ca 2+ ions for the formation of reaction rims, so that the ASR expansion decreases after passing the pessimum proportion. Very fine reactive aggregate and admixtures with the grain size less than ~ 50 µm preferentially react with alkali hydroxide to convert to mature alkali silicate without leaving any reactive minerals. Homogeneous mixing of the sufficient amount of very fine siliceous admixtures in concrete therefore inhibits the ASR by absorbing Ca 2+ ions for the rim formation. The resultant fragmental calcium silicate fills the pores in concrete to increase the strength and the durability of the concrete. The admixtures thus act as pozzolanic materials.

Influence of Alkaline Earth Silicate Admixture on Durability of Pennsylvania Turnpike Bridges

Chlorides from deicing salts are the primary cause of premature corrosion of reinforcement in concrete bridge decks. An alkaline earth silicate admixture (AESA) can reduce the permeability of concrete, preventing the ingress of chlorides, delaying the onset of rebar corrosion, and therefore increasing the design life of bridges. The performance of an AESA in bridge decks that have been in service for more than 25 years is compared with the performance of identical control bridges of comparable age. Visual inspection reveals serious deterioration in the control specimens. The decks of the control bridges reveal cracks, delaminations, and spalling in many of the precast deck panels. In the bridges with AESA, there is minimal visible deterioration. The goal of this research is to identify and characterize the effect of AESA on inservice bridge decks. Chemical and microscopic techniques are used to determine the nature of AESA in hardened concrete. Water and chloride ion permeability tests are performed to quantitatively determine the relative effects between control concrete and concrete containing the AESA. Testing has shown that AESA has chemical characteristics that enable it to react with portland cement and control the microstructural development in concrete. Quantitative tests for permeability and environmental scanning electron microscopy (ESEM) reveal a microstructure that is more continuous and interlocked than that of the control samples, indicating that the AESA reacts with cement to provide a microstructure that is less permeable.

Fly ash and slag: standards and specifications—help or hindrance?

From technical, economic and ecological points of view, siliceous by-products are now recognized and accepted as desirable and vital constituents of concrete. Current specifications for such materials tend to be restrictive to some extent, however, and in many countries there are separate standards for each admixture. These in turn inhibit the wider use of these mineral additions to concrete. This paper presents a review of the more important aspects of current standards for siliceous admixtures in this context. It is shown that there is not only a lack of uniformity in the requirements of these standards, but also wide variations in the limits set for a given requirement. It is suggested that these variations reflect not only the industrial or agricultural background of the by-products but also the inevitable wide range of compositions arising from it. The paper discusses selected items of specifications such as alkali contents, the role of physical properties and mineralogical compositions in the development of strength, the relationship of composition to hydraulicity and the relevance of the pozzolanic and slag activity index tests. Guidance is given on the development of a reliable slag activity index test related to its performance in concrete. An accelerated test is also recommended as an acceptance criterion. The integrity and durability of concrete structures is closely linked with the characteristics of the materials used, but there is no clear understanding of this interrelationship with design and construction. Under these circumstances, material specifications are likely to be prescriptive and sometimes restrictive. The need, however, to correlate requirements for quality control and quality assurance with the real performance of the concrete in the structure cannot be overemphasized. The paper proposes a more positive and engineering-oriented approach to the use of these materials in concrete, so that a wider range of the applications of concrete in practice can incorporate these mineral admixtures as partial cement replacements.

Fly ash and granulated blast‐furnace slag as ‘stabilisers’ of portland cements with added periclase

AbstractOne method proposed for utilisation of high‐magnesia Portland cements involves the addition of active siliceous admixtures such as fly ash or ground granulated blastfurnace slag. This addition enables otherwise unsound cements to pass the ASTM autoclave test (C151–74a) for expansion of Portland cement. Cements were made from an OPC, magnesia (2 and 3%) and varying proportions (0–70%) of fly ash or ground granulated slag. The expansions of pastes made from the cements stored at 50°C were measured over periods of 3 and 4 years, respectively. The cements were also subjected to the ASTM autoclave test. The results of the autoclave test support the view that expansion in the autoclave is to some extent related to the strength of the matrix, and best results were obtained with CaO:SiO2 ratios of about 1.25 corresponding to formation of large quantities of 1.1 nm tobermorite. However, it has been shown that even a high strength matrix cannot stabilise too much free magnesia either in the autoclave or at 50°. Slag was less effective than fly ash in producing a reduction in autoclave expansion although results at 50° were comparable. This work on cements with added periclase suggests that the stabilisation of ‘normal’ high magnesia cements, in both the autoclave and under more normal conditions, with any practical level of stabiliser addition, will depend on factors such as the ‘blocking effect’ described by Rosa, and the dilution effects of stabiliser addition being sufficient to reduce the effective free magnesia content to the small amount which the strength of the matrix can control.

Studies on Pozzolanic Materials as Portrand Cement Admixture, (III)

On continuing the previous studies (This Journal, 62 [696] 403-406 (1954); 63 [714] 523-527 (1955)), the authors report in the present paper the results of further studies on various properties of fly ash by comparing with other siliceous pozzolanic admixtures used in the previous reports (loc. cit.). The collected samples were three kinds of fly ash from electric power plants (Chicago fly ash from America, Ube fly ash from the Ube Kosan Co., and KFA fly ash from the Kansai Denryoku Co.), one coal ash KPA quenched in water pond from the Kansai Denryoku Co., and two kinds of natural siliceous pozzolanic materials (Beppu-hakudo and Oya-ishi used in the previous reports (I) and (II)). These samples were analysed and compared by the common total and special soluble analysis. The testing of lime-adsorption and the electron microscopic photographs gave clear difference between fly ash and natural siliceous pozzolanic materials. The test of swelling in distilled water or in lime water, the alkalinity test, the bending and compressive strength tests by the standard 1:2-cement sand mortar, and the bleeding test (ASTM Proc., 49, 891 (1949)), etc., gave clear aids for the discrimination between true fly ash, pond ash and other siliceous admixtures.

Studies on Pozzolanic Materials as Portland Cement Admixtures, (II)

On continuing the previous studies (This Journal, 62 [696] 403-406 (1954); 63 [714] 523-527 (1955)), the authors report in the present paper the results of further studies on various properties of fly ash by comparing with other siliceous pozzolanic admixtures used in the previous reports (loc. cit.). The collected samples were three kinds of fly ash from electric power plants (Chicago fly ash from America, Ube fly ash from the Ube Kosan Co., and KFA fly ash from the Kansai Denryoku Co.), one coal ash KPA quenched in water pond from the Kansai Denryoku Co., and two kinds of natural siliceous pozzolanic materials (Beppu-hakudo and Oya-ishi used in the previous reports (I) and (II)). These samples were analysed and compared by the common total and special soluble analysis. The testing of lime-adsorption and the electron microscopic photographs gave clear difference between fly ash and natural siliceous pozzolanic materials. The test of swelling in distilled water or in lime water, the alkalinity test, the bending and compressive strength tests by the standard 1:2-cement sand mortar, and the bleeding test (ASTM Proc., 49, 891 (1949)), etc., gave clear aids for the discrimination between true fly ash, pond ash and other siliceous admixtures.

Studies on Mixed Portland Cements, XII

The authors reported, in continuing the previuos studies on mixed Portland cements, the results of further comparative tests on high silica mixed Portland cements. The following summaries were abstracted from the original Japanese paper.(1) Three sorts of natural siliceous earth, which are called “Keisan-hakudo, Yokei-hakudo and Kayo-hakudo”, and these are kinds of siliceous sinter obtained plentifully in volcanic districts. The following table 1 is the results of the total analysis and the table 2 shows the results of insoluble and soluble parts treated by 10%-NaOH and 5%-HCl solutions.Table 1. Results of Total Analyses of Samples of Siliceous EarthTable 2. Results of Soluble Analyses of Samples of Siliceous Earth(2) Two sorts of Portland cement clinker were used to mix with these siliceous earths and ground to high silica mixed Portland cements. The mixing proportions and physical properties of the prepared cement samples were compared in the following table 3.Table 3. Mixing Proportions and Physical Properties of High Silica Mixed Portland CementsHigh silica mixed Portland cements have considerably small values of specific gravities, owing to the small specific gravities of high siliceous admixtures.(3) The chemical compositions of these cement samples were analysed and the results are shown in the following table 4.Table 4. Chemical Compositions of High Silica Mixed Portland CementsMixed Portland cements contain considerably large amount of insoluble residue in hydrochloric acid. Total silicic adi dexceeds 45-50%, so that these cements will be called silica cement, high silica cement or high silica mixed Portland cement. Total lime is, on the contrary, very little and does not exceed 35-43%(4) These samples were tested on their compressive and tensile strengths of 1:3-cement-sand mortars by the method described in the “Japanese Engineering Standard” for Portland cement (JES 28) or for blast furnace slag cement (JES 29). The results are tabulated in the following table 5.Table 5. Results of Tests on Compressive and Tensile Strengths of 1:3-Cement-Sand MortarsThese test by the so-called “dry mortar” of the standard specification is very favourable for these high silica mixed Portland cements and gives considerably large strengths, especially the tensile strengths. These ordinary strengh tests are not suitable to discuss the mixed Portland cements. So that, the authors studied already on the plastic or wet mortar test, which is the modified method from the Haegermann's method (G. Haegermann: “Die Pruefung plastischer Moertel”, Protokoll der Tagung des Vereins deutscher Portland-Zement Fabrikanten, E. V., Sept. 1929, S. 35; “Die Zementpruefung bei Anwendung von Moertel mit hochem Zementzusatz”, Report of the New International Association for Testing Materials, Zuerich, 1931, p. 669) and the Roš's method (Prof. M. Roš: “Die zukuenftigen schweizerischen Norman fuer Bindemittel auf Grundlage von Untersuchungsergebnissen der E. M. P. A. (Eidg. Materialpruefungsanstalt) an der Eidg. Tech. Hochschule in Zuerich: Die Pruefung der Zemente mit plastischer Moertel”, Diskussionsbericht Nr. 1, Mai 1925, Nr. 10, April 1926, and Nr. 60, September 1931). The plastic mortar is from cement: fine sand (sea sand for sheet glass industry in Japan, which is obtained from Korea and has the fineness of 400M/cm2-3600M/cm2): Japanese standard sand in the proportion of 1:1:2 and 60-70% of water-cement ratio, which will be determined by the small flow table and the flow of 200%. The results are shown in the following table 6.Table 6. Results of Tests on Compressive and Bending Strengths of Plastic MortarThese results from the plastic mortar tests are more suitable to compare Portland cement,