Portland Cement Mixes Research Articles

Structural properties of sepiolite-reinforced cement composite

The structural properties and optimum blend ratios of sepiolite-reinforced cement composites are investigated. It is shown that the addition of 10% sepiolite (a natural clay mineral) fibers enhances the mechanical and physical properties of the mortar. In comparison to the ordinary Portland cement mix, improvements of 3.5%, 6.2% and 7.7% in compressive strength and 12.7%, 5.7% and 6.3% in bending strength values were respectively obtained for 2, 7 and 28 days. Based on the scanning electron microscope pictures, this enhancement is attributed to the modification of the rheology of the mortar through sepiolite fibers inducing a network structure within the cement matrix.

Sample Preparation Technique for Artificially Cemented Soils

Abstract Design of offshore foundations in cemented calcareous sediments requires a full understanding of the strength and deformation properties of the cemented soils. However, obtaining natural undisturbed samples from offshore sites is very expensive, and so there is a need to prepare reconstituted soils in the laboratory to replicate the natural material. Traditionally, cementing of the soils has been modelled by mixing Portland cement or gypsum powder with the uncemented soil in appropriate proportions to obtain a given strength. This note describes a new sample preparation technique to provide high quality lightly-cemented samples of consistent density. Although the technique is suitable for many different forms of cementing agents, it is used here in conjunction with the Calcite Insitu Precipitation System (CIPS), where cementation is effected by flushing a special solution through the soil, leading to precipitation of calcite on the soil grains. This leads to a form of cementation that simulates the natural material much more closely than using conventional particulate cementing agents. The sample preparation technique is described, and example results are presented for a range of soils. Comparisons are given between the stress-strain response of CIPS-cemented and Portland-cemented soil, with the former exhibiting more brittle behavior after failure, and a greater tendency for volumetric collapse.

Electrical properties of fluidified Portland cement mixes in the early stage of hydration

The electrical conductivity and the dielectric constant of cement mixes have been studied in the initial stages of setting to correlate the time evolution of the electrical parameters with the chemical and microstructural modifications. The formulations, based on a mix of Portland cement and microsilica, were fluidified with various amounts of an acrylic polyelectrolite and had a w/c ratio of 0.24. Measurements were carried out at ambient temperature for times of up to 40 h, in the frequency interval 30 Hz–200 kHz. The conductivity showed a marked decrease correlated with the loss of connectivity of the macroscopic porosity (depercolation). The time to the drop of conductivity depended linearly on the concentration of superplasticizer whose retarding effect was clearly evidenced. A dielectric amplification phenomenon was observed which vanished after the porosity depercolated. The temperature profiles of mixtures with different concentrations of the superplasticizer were drawn and a simple model was developed to compute the specific thermal power as a function of time. A substantial coincidence was found, on the time axis, between depercolation and maximum rate of setting. Vicat tests were also carried out.

The influence of ground granulated blastfurnace slag (GGBS) additions and time delay on the bleeding of concrete

Bleed tests were performed in accordance with ASTM C232-92 on concretes in which up to 85% of the cement was replaced with ground granulated blastfurnace slag (GGBS) obtained from a number of different sources. The time at which the bleed test was started was varied from 30 to 120 min to simulate site conditions. The addition of up to 55% slag increased the bleed capacity by 30% (compared to the plain Portland cement (OPC) mix) but had little effect on bleed rate. Increasing the slag content to 85% had no further significant effect on bleeding. The source of slag was also found to have little effect on the bleeding but comparisons made with results from 10 years ago suggest that now the present day slags have a much less marked effect on bleeding probably because they are ground finer. Delaying the start of the bleed test from 30 to 120 min reduced the bleed capacity of the OPC mix by more than 55% compared with 32% for the slag mixes. The reduction in bleed rate was similar for all mixes at about 45%.

Limes And Lime Mortars—Part One

This paper deals with limes and lime mortars and is presented in two parts. Part One identifies the sources and qualities of limes in England and Wales and then proceeds to trace the burning of lime, the development of kiln design and the search for hydraulic cements from ancient times up to the end of the nineteenth century. Part Two, which will appear in the next issue of the Journal, examines the slaking and use of lime for mortar mixes and compares the qualities of lime-based mortars with composition and ordinary Portland cement mixes. General advice is offered on mortar mixes for the repair of historic fabric and three case studies are provided to illustrate the importance of determining appropriate mortar compositions for repair work.

Cracking in Exterior Insulation and Finish Systems

The outside lamina of an exterior insulation and finish system is typically applied as a plaster using a polymer and portland cement mix, reinforced by a mesh that is usually a glass fiber product. Observations of leakage and cracking are discussed. Engineers sometimes find a particularly severe cracking failure in which the crack splits the system, including the mesh, fully through its thickness, suggesting that in such cases the mesh is of insufficient strength to distribute tensile strains and control cracking. Elementary stress analysis establishes the conditions under which such full splitting will occur. Pilot tests were performed to measure elastic modulus, rupture stress, shrinkage strain, and mesh strength. For the sample system studied, the measured properties confirm the mesh strength to be inadequate for control of cracking, and predict system performance failure by full splitting. Further analysis demonstrates that the tensile strain field producing such failure can be produced solely by shrinkage of the material.

Measurement of chloride penetration into silica fume concrete

Chloride induced corrosion is a major factor affecting the service life of concrete structures. The likely effect of using silica fume to reduce chloride penetration has been measured using a ponding type experiment and an electrical method. It is concluded that due to the special properties of the silica fume mixes the electrical test is not a reliable way of measuring the effect but they are less permeable than the ordinary portland cement mixes.

Comparison of Latex-Modified Portland Cement Mortars

The paper compares the properties of latex-modified portland cement mortars made using 5 different types of latex that are commonly used as admixtures for portland cement mixes. Selected colloidal and polymeric properties of latexes are described. The latex modified mortars are compared for water-cement ratio, permeability, adhesion, compressive strength, flexural strength, weathering resistance, freeze-thaw resistance, acid resistance, and carbonation resistance. The results are discussed, and recommended applications for the various latex types of modifying mortars are suggested.

Pore Structure, Permeability, And Chloride Diffusion In Fly Ash-And Slag-Containing Pastes And Mortars

AbstractThe transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.

Pore Structure, Permeability, and Chloride Diffusion in Fly Ash-and Slag-Containing Pastes and Mortars

ABSTRACTThe transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.

Ordinary Portland Cement Mixes With Selected Admixtures Subjected to Sulfuric Acid Attack

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Strength and deformation characteristics of an acrylic polymer-cement composite

The time-dependence of strength and deformation properties of an Acrylic polymer modified concrete has been investigated up to 600 days under wet and dry curing conditions. Ordinary Portland Cement mixes of proportion 1:2:3 (by weight) were used and the water cement ratio was adjusted in order to achieve reasonably constant workability for the control and modified mixes.

High‐pressure steam curing of high‐slag cement. II. Strength of cement‐sand mixes

AbstractThe strength of dense high‐slag cement‐sand mixes autoclaved at 180 lbf/in2, and of certain aerated mixes autoclaved at pressures ranging from 120 to 210 lbf/in2, has been determined. It was found that maximum strengths were developed in an autoclaving period of 5 h at 180 lbf/in2, and that longer periods, as well as higher autoclaving pressures, yielded lower strengths. The maximum strength values obtained for compacted 1: 3 (w/w) mixes were 425 kg/cm2 in the absence of fine quartz, and 510 kg/cm2 in the presence of suitable addition of fine quartz. The corresponding values for Portland cement mixes were, respectively, 330 and 460 kg/cm2 for a heating period of 5 h, and 360 and 505 kg/cm2 for a period of 6 h.

Mixing-In-Place Soil and Portland Cement

Construction methods can be found to mix portland cement grout and soil in place below ground at the rate of 1,000 cu yd a day at $8 to $15 per cu yd. When such methods and apparatus are developed, there will be widespread application in the field of underground construction. Among the more important applications may be stabilizing sand deposits under nuclear power plants in earthquake regions.

Aggregates and Fly-Ash Concrete for Barkley Lock

Discussion of handling and mixing of aggregates of fly-ash concrete for Barkley Lock, Kentucky; methods and equipment used for separation of Ohio River sand into various sieve fractions, reworking of certain sieve fractions, and recombining of fractions for completed sand; results of testing; automatic concrete batching and mixing plant and portland cement silo.

ON THE VOLUME CHANGE OF FLY ASH MIXED CEMENT

The author studied the drying shrinkage of specimens at constant relative humidity of 44% about several kinds of cement. As a result comparing the drying shrinkage of fly ash mixed portland cement (mixing proportion by weight P.C.: F.A.=80:20) with those of normal portland cement, high early strength portland cement, moderate heat portland cement, natural pozzolana cement, slag cement, the volume change of the fly ash cement has been found always the smallest.The author also tested the differences of cracking tendency by so-called ring test, comparing with the portland cement types I, II, III and those cements in which 20% or 30% fly ash was mixed in each of I, II, III type portland cements. It was observed that type II cement mixed with 30% fly ash showed the smallest tendency of crack corresponding to the least values of shrinkage and modulus of elasticity.

STUDIES ON AUTOCLAVE TESTS OF VARIOUS CEMENTS, II

The author, in continuing the previous study (This Journal, 1938, Vol. 38, No. 584, p. 397-p. 403), studied further on the autoclave test for soundness and expansion or contraction of cement or cement-sand mortar. This testing method was applied on various kinds of Portland cement and mixed Portland cement for various purposes, i.e., (1) Testing expansion or contraction, (2) Bending strength, and (3) Compressive strength from the same test pieces by using 4×4×16cm prismatic test pieces of plastic mortar, which results are briefly abstracted from the original Japanese communication, as following:(1) Cement samples were selected for studying on the value of autoclave test, especially for testing on the relation between the soundness and chemical compositions of various cements. Three samples of common Portland cement, three of low-heat or modified Portland cement, three of high iron oxide Portland cement, one of blast furnace cement, and five of high silica mixed Portland cement, so that totally fifteen samples of various kinds of cement were selected for the present study.(2) These cement samples were first compared their chemical compsiotions and various physical properties. The strength tests were also carried out in two ways, (1) the dry or non-plastic mortar of 1:3-cement and standard sand for Portland and blast furnace cements (JES 28 and 29) of Japanese Engineering Standards, and (2) the wet or plastic mortar of 1:2-or 1:1-cement and fine sand.(3) Beam test pieces (4×4×16cm) ot wet of plastic 1:2-cement and fine sand mortar were treated, after seven days common water curing, in hot water under steam pressure (5kg/cm2 and about 152-153°C or 30kg/cm2 and about 227-228°C) in autoclave for two hours, and measured the expansion or contraction after cooling in water of room temperature and atmosperi pressure. The results were sufficient to make clear the differences between various cements, especially the unsoundness of high iron oxide containing special Portlant and soundness of high silica containing mixed Portland cement by mixing about 30% of proper admixture containing large amount of soluble silica.(4) After this measurement of expansion, the beam test pieces were tested on their bending strength or modulus of rupture and then compressive strength, and these results were compared with those obtained in the above section (2) by the common curing in water of room temperature and atmospheric pressure. These comparisons are useful to discuss various mixed Portland cements being better than special Portland cements of high iron oxide or silica content.(5) Neat cement paste was tested by the LeChatelier's calliper method curing in autoclave as above mentioned and the increase of opening of calliper was compared to discuss various samples of mixed Portland cement being better than simple Portland cements containing large amount of iron oxide or silica.

STUDIES ON AUTOCLAVE TESTS OF VARIOUS CEMENT, Part I

As the testing method of soundness of cement is commonly used neat cement or cement paste, e.g., (1) the qualitative test of observation of cracks on pat from neat cement paste curing for 28 days in water or boiling, or (2) the quantitative test of measuring expansion or contraction of neat cement paste of prismatic test piece by the Bauschinger's method or of cylindrical test piece by the LeChatelier's method. These tests are to be commonly carried out under atmospheric pressure, but there are seen some literatures relating to high pressure testing or autoclave test of soundness of cement, and this test was recently seen to be adopted as the standard method by the American Portland Cement Association Fellowship (Cement and Lime Manufacture, 1937, 10, No. 5, 129; R. N. Young, Journ. Amer. Concrete Institute, Vol. 34, Sept. -Oct., 1937; N. C. Rockwood, Rock Products, 1938, 41, No. 1, 85, ect.).The present author proposed before 10 years the plastic mortar method, as the new cement testing method instead of the present method of dry mortar in the Japanese Portland and blast furnace cements standards (JES 28 and 29), and was studying on this method for various purposes, i.e., (1) Testing of bending strength, (2) Testing of compressive strength, (3) corrosion by salt solution or sea water, (4) Expansion or contraction cured in water or various salt solutions at the room temperature or by boiling, and (5) Soundness test cured under high pressure steam or autoclave test, which results are briefly abstracted from the original Japanese communication, as following:(1) Cement samples were selected for the purpose of comparison of autoclave test, especially for the studying on the value of autoclave test to discuss the relation between the soundness and chemical compositions of various cements. Two samples of common Portland cement, three of high magnesian Portland cement, two of blast furnace cement, one of high silica mixed Portland cement, and two of high alumina cement first produced in Japan (S. Nagai, Journ. of Japanese Ceram. Assoc., 1938, 46, 123), so that totally ten samples of various kinds of cement were selected.(2) These cement samples were first compared their chemical compositions and various physical properties, as in the foregoing studies, on variousc ements, e.g., specific gravity, fineness (residue on 4900meshes/cm2-sieve), voids, setting time, etc. The strength tests were also executed in two ways as adopted in the foregoing reports, i.g., (1) by ths dry or non-plastic mortar of 1:3-cement and standards sand in the Japanese engineering standards of Portland and blast furnace cements (JES 28 and 26) and (2) by the wet or plastic mortars of 1:2-or 1:1-cement and fine sand.(3) Neat cement paste was first tested by the LeChatelier's method but by heating in autoclave, i.e., the increase of opening of calliper was compared by treating in the superheated steam of 153-155°C and about 5kg/cm2 steam pressure for two hours. The increase of the calliper opening was not over 3-3.5mm, which is smaller than the limit 5-6mm in the common test under atmospheric pressure by the LeChatelier's method. So that, it is clear that the steam pressure 5kg/cm2 of the autoclave test is not sufficient and is necessary to test under higher steam pressure than 10 or 15kg/cm2 (and about 182-183°C or 200-202°C), which will be tested and reported in the next report.(4) Beam test pieces (4×4×16cm) of wet or plastic 1:2-cement and fine sand mortar were treated in the autoclave of superheated steam pressure of 5kg/cm2 and about 153-455°C for 2 hours, and measured the expansion of distance between two points on the test beam by the comparator of micrometer type. The results were sufficient to compare the unsoundness or large expansion 10-15mm/10m of high magnesian Portland cement with those (3-5mm/10m) of smaller expansion of other cements.(5) After

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 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,