Pozzolanic Portland Cement Research Articles

Fresh Properties of Mortar made with Pozzolanic Cement and Water Reducers

ABSTRACTNatural pozzolans are supplementary cementitious materials (SCMs) that may be used to improve the properties of mortar and concrete, through the formation of additional hydration products by pozzolanic action. Water reducers (WR) play a main role in high performance concrete in terms of durability, strength and surface finishing. A first optimization of constituent proportions in paste and/or mortar is convenient to assess the compatibility between the WR and the cementitious materials. The compatibility between cement and WR may be affected by SCMs, as they can also interact with the molecules of the admixture. However, the practical implication may be variable. This paper deals with the influence of different types and dosages of WRs in mortars made with pozzolanic Portland cement. Both medium and high ranges WRs have been used. Mortar fluidity has been tested by the spread and the slump tests. Results show different fluidizing capacities of WRs, among which polycarboxylate-based WR was the most compatible with the pozzolanic cement.

Toughness increase of self compacting concrete reinforced with polypropylene short fibers

Increases in bending tests by the addition of low volume fractions of Polypropylene (PP) Short Fibers PP. These toughness increases are similar to those attained by Fiber Reinforced Concrete (FRC) referred elsewhere as Engineered Cementitious Composites (ECC), having some ductility and strain hardening in direct tensile and flexural tests. Concretes mixtures were manufactured using natural pozzolanic blended Portland cement, volcanic crushed coarse aggregates and fine sand from Sahara desert dunes (0-1 mm) from Canary Islands quarries and sand reservoirs, respectively, besides ordinary siliceous sand (0-4 mm) and fly ash from an anthracite-coal heat generator.

Characterising cement–superplasticiser interaction using zeta potential measurements

The zeta potential generated at the interface between cement particle surfaces adsorbed with superplasticisers have been studied using electroacoustic technique, which is capable of measuring zeta potential at high concentrated suspensions. The study has been undertaken to examine the differences in the magnitude of the zeta potential for ordinary Portland cement (OPC) and Portland pozzolanic (fly ash) cement (PPC) pastes along with the differential impacts of different types of superplasticisers on both the varieties of cement pastes. In the latter context, the effects of three different types of superplasticisers namely Ligno Sulphonate (LS), Sulphonated Melamine Formaldehyde (SMF) and Sulphonated Naphthalene Formaldehyde (SNF) have been specifically studied. The results show that the cement pastes with PPC shows better dispersion when compared with the OPC. The paper also endeavors to unfold the relationship and significance of cement interaction with three different superplasticisers.

Engineering Innovation at Bonneville Dam

The United States Army Corps of Engineers constructed Bonneville Dam on the Columbia River in the 1930s to improve river navigation and provide hydroelectric power to the Pacific Northwest. This paper demonstrates how the Corps’ approach to the planning and design of the dam’s structures, machines, materials, and processes fostered engineering innovations. These innovations included a new kind of concrete, a portland-pozzolan cement mix that reduced temperature-induced cracking in the massive structure; a new spillway design incorporating energy dissipating structural features; and a new kind of water turbine that enabled efficient power production under widely variable hydraulic flow conditions, adjustable-blade Kaplan turbines. The Corps’ success in the development of innovative engineering designs at Bonneville Dam illustrates the central role of civil engineers in the process of planning, designing, and building major public works.

Effectiveness of shrinkage-reducing admixtures on Portland pozzolan cement concrete

Drying shrinkage causes tensile stress in restrained concrete members. Since all structural elements are subject to some degree of restraint, drying shrinkage is regarded to be one of the main causes of concrete cracking. The purpose of the present study was to evaluate the effectiveness of SRA in reducing drying shrinkage strain in Portland pozzolan cement concrete. The major variables examined included slump, admixture type and dose, and specimen size. The measured results indicate that any of the admixtures used in the study significantly reduced shrinkage. Concrete manufactured with shrinkage reducing admixtures shrank an average of 43% less than concrete without admixtures. As a rule, the higher the dose of admixture, the higher was its shrinkage reduction performance. The experimental results were compared to the shrinkage strain estimated with the ACI 209, CEB MC 90, B3, GL 2000, Sakata 1993 and Sakata 2001 models. Although none of these models was observed to accurately describe the behaviour of Portland pozzolan cement concrete with shrinkage reducing admixtures, the Sakata 2001 model, with a weighted coefficient of variation of under 30%, may be regarded to be roughly adequate.

Properties and Utilization of Zeolite-Blended Portland Cements

AbstractThe resistance to acidic and sulfate attack of Portland-pozzolan cement containing 35 wt.% of zeolite was compared with that of unamended Portland cement. Mortar specimens kept in 0.5% and 1.0% HCl solution, 5% Na2SO4 solution, and in reference water for 365 and 720 days were tested using a set of physical-mechanical and chemical techniques. The ability of mortars containing zeolitic cements with 15 to 50 wt.% of zeolite to protect steel against corrosion was verified by a potentiodynamic method. Mortar with zeolitic cement performs better when exposed to 1% HCl solution due to the presence of a finer pore matrix, a hydrate phase poorer in CaO-containing hydration products with lower leachability, and the high resistance of zeolite material itself to acidic attack, compared with Portland cement and siliceous sand. The improved sulfate resistance of the mortar with zeolitic cement is caused by the decreased C3A in the cement blend in comparison with that in Portland cement, a reduction in SO3 binding into the cement paste and decreased amount of CaO-containing hydration products capable of reacting with a sulfate solution forming voluminous reaction products, and consequent crack propagation, large expansion and structural disintegration. Passivation of steel in mortars with blends of Portland cement to zeolite percentage ratios of 85/15, 75/25 and 65/35 by weight is comparable to that of Portland cement mortar. This is particularly important because the mortar with zeolitic cement exhibits late strengths similar to that of Portland cement mortar. This confirms that zeolitic cement can replace Portland cement in many applications with the advantage of higher resistance to acidic and sulfate attack.

Hydration of portland cement, natural zeolite mortar in water and sulphate solution

The objective of this paper is to characterise sulphate resistance of mortars made from ordinary Portland cement ( PC ) and Portland-pozzolan cement with 35 wt.% of zeolite addition (zeolite-blended cement-ZBC ). Mortars with two different cement types were tested in water and 5% sodium sulphate solution for 720 days. A favourable effect of zeolite on increased sulphate resistance of the cement is caused by decrease in free Ca(OH) 2 content of the mortar There is not sufficient of Ca(OH) 2 available for reacting with the sulphate solution to form voluminous reaction products. A decreased C 3 A, content due to 35 wt.% replacement of PC by zeolite is the next pronounced factor improving resistance of the mortar with such blended cement.

Physical, mechanical and microscopic characterization of cold bonded fly ash lightweight aggregates

This study presents the results of the different tests carried out on fly ash lightweight aggregates produced with three different kinds of binders: Lime, Portland cement and Pozzolan Portland cement. The elaboration process used for the aggregates consisted in an agglomeration system by agitation under cold bonded hardening conditions. The tests carried out were a physical characterization of the aggregates, the determination of mechanical properties with a crushing test and, finally, the study of the microstructure of the aggregates with scanning electron microscopy (SEM) and dispersive energy X ray (EDX). From the point of view of mechanical strength, the results indicate that the best kind of aggregate is the one made with a 5% Pozzolan Portland cement. This result was confirmed by the microstructure analysis, which shows that this kind of aggregate presents the highest hydration speed.

Importance of using the natural pozzolans on concrete durability

Natural pozzolans have become important because of their role in concrete durability. This situation has provoked an increase in the use of pozzolanic cement in concrete construction. This paper reports results of different portland–pozzolan cements containing different natural pozzolans, and they were compared with ASTM Types I, II and V cements. The pozzolanic activity and composition of each pozzolan were evaluated. The susceptibility to sulfate attack was studied by measuring the expansion in mortar bars at different ages (according to ASTM C 1012 Method) for 78 weeks. It was found that certain cements containing pozzolans with high activity or low alumina content improve resistance to sulfate attack, although the amount of pozzolan in the cement is important.

Potential use of phosphogypsum in concrete

An experimental study was conducted to investigate the potential use of phosphogypsum (PG) in concrete. This was accomplished by preparing mortar mixes at a water/cement ratio of 0.6 using two types of cement, ordinary Portland cement (OPC) and pozzolanic Portland cement (PPC), and two types of fine aggregate, natural river sand and limestone. These mixes were prepared at different replacements (by weight) of PG and purified PG ranging from 10–100%. The purified PG was obtained by calcining PG (washed in water and not washed) at temperatures of 170, 600, 750, 850, and 950°C. The compressive, tensile, and flexural strengths of different hardened mortars were obtained following 3, 7, and 28 days of curing in air and in a moist room. In addition, the setting time and the soundness of cement pastes, prepared using OPC and PPC at a water/cement ratio of 0.6 and at different replacements of PG, were evaluated. At a particular PG percentage of replacement, the results indicated an increasing trend in strength gain over curing time. The strengths of mortars, cured for a specific time, showed a decrease in the strength with further replacement with PG. The purification process, by heating PG up to 900°C, has resulted in improving the strengths of the mortar mixes. The highest percentage increase in strength was found to be for PG calcined at temperatures of 850 and 900°C. The incorporation of PG in the cement paste has dramatically increased its initial and final setting times and has increased the percentage elongation of paste prisms used to evaluate the soundness. The improvement in strength upon calcination is primarily due to the formation of anhydrate at higher temperatures, which subsequently hydrates to gypsum; the latter has some cementing value.

Development of a multiple linear regression model for predicting the 28-day compressive strength of Portland pozzolan cement

A multiple linear regression model was developed for the prediction of the 28-day compressive strength of Portland Pozzolan Cement (PPC) containing Santorin Earth as an admixture. The independent variables of the model were: (1) the compressive strength at the age of 2 days, (2) the compressive strength after autoclave hydrothermal treatment at 2.07 N/mm2 (300 psi) and 214°C for 3 h, (3) the C3S/C2S ratio of the clinker, (4) the insoluble residue of the cement, (5) the pozzolanic activity factor and (6) the C3A content of the clinker. The evaluation of the proposed model was performed by various statistical tests, all of which were successful. These tests included: multiple correlation, test of the significance of coefficients (t-test), estimation of confidence intervals for coefficients, test for outliers and unusual residuals, test for influential points, conditional sums of squares, R-squared and analysis of variance. There was very good agreement between the strength predicted by the multiple regression model and experimental results.

Properties of pastes, mortars and concretes containing natural pozzolan

Laboratory tests were conducted to investigate the effects of a local natural pozzolan on certain paste, mortar and concrete properties when used as a separate admixture or interground in amounts more than used in the commercial pozzolanic portland cement (i.e. more than 15% by weight).The pozzolan was ground in two levels of fineness and was used together with some local cements. According to the results the finer pozzolan was more active. It could be added upto 25% by weight of cement without reducing the 28 day strength. At 35% admixing levels the strength of ordinary portland could be matched at around 90 days. Pozzolanic addition reduced the heat of hydration, somewhat prolonged the setting times and improved the soundness of cements. It caused some increase in mortar shrinkage and slightly reduced the workability of mortars and concretes. Based on the test results the use of the natural pozzolan as a separate concrete admixture and as an addition in the production of a family of blended local cements are recommended.

Effect of initial water curing on the hydration of cements containing natural pozzolan

This paper deals with the effect of initial curing conditions on the hydration process of Portland pozzolan cements. Experiments were performed on pastes made with Canadian Standards Association (CSA) Type 10 (ASTM Type I) Portland cement (PC) and Portland pozzolan cement (PPC) containing 30% natural pozzolan by mass. PC pastes are more sensitive than PPC pastes to the period of initial water curing because the hydration of PC occurs more quickly than does the pozzolanic reaction in PPC pastes. The hydration of Portland cement and the pozzolanic reaction continue after specimens are removed to a dry environment (relative humidity ≈ 20%). The presence of natural pozzolans retards the normal hydration of PC before an age of 1 day but accelerates it after 1 day. For the tests reported here, an excellent correlation exists between strength and the quantity of “hydrate” water. The measurement of pore structure shows that the measurable total pore volume is significantly decreased for specimens that are water-cured and then dried, compared with those that are water-cured only. The period of initial water curing does not have a significant effect on total pore volume at 28 days (measured by Hg porosimetry), but does affect the pore size distribution. Examination of strength is not a good indicator of the effect of initial water curing.

The effect of various types of cement dust on sulphur dioxide oxidation in the air

The effect of various types of cement dust on the behaviour of sulphur dioxide in the air was investigated on model systems in different experimental conditions.Experiments were carried out with PC-15z-45s (Portland-blast furnace cement containing 15% blast furnace slag), PC-25p-35s (Portland-pozzolan cement containing 25% pozzolan) and EFD (electrofilter dust).EFD most effectively removed SO2 from the air stream. The next efficacious was PC-15z-45s, whereas PC-25p-35s was the least efficient. The efficacy of cement dusts for SO2 removal from the air stream depended on their chemical and granulometric composition and in particular on the size of specific surface.The rate of reaction was also influenced by experimental conditions-relative humidity, the length of contact, that is, the flow rate of gaseous mixture through the reactor, and the amount of cement dust.The experimental data show that in the contact between SO2 and cement dust catalytic oxidation of SO2 to sulphates takes place. Sulphates remain bound to the surface, from which they cannot be thermally desorbed, but can be released by extraction in the Soxhlet apparatus.

Accelerated Strength Testing of Portland-Pozzolan Cement Concretes by the Warm Water Method

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Studies on blended Portland cements containing Santorin earth

Although pozzolans, such as the Santorin earth, have been in use for over two thousand years for making cementitious products, the mechanism by which pozzolanic reactions contribute to the strength and chemical durability of mortars and concretes is not fully understood. Reported here are the results of an investigation in which portland pozzolan cements containing 10, 20, or 30 weight percent Santorin earth were used. Performance of the cements was evaluated with respect to strength development, drying shrinkage, sulfate resistance, and alkali-silica activity. The cement containing 20 percent pozzolan showed the highest compressive strength at 1 year, and the cements containing 20 or 30 percent pozzolan showed the least permeability and best resistance to sulfate attack. Microstructural investigations involving scanning electron microscopy, X-ray diffraction analysis, determination of free Ca(OH) 2 present, and pore-size distribution were conducted on hydrated cement pastes for the purpose of understanding the factors responsible for the observed behavior of the cements. From the results, it is concluded that the process of pore refinement associated with pozzolanic reactions plays an important part in enhancing the strength and chemical durability of portland pozzolan cements. It is suggested that the rate at which pore refinement occurs in a hydrating pozzolan cements is not only useful as a measure of the activity of the pozzolan presen, but also for a more reliable prediction of the performance characteristics of the cement.

コンクリートの中性化と鉄筋のさびについて

Experimental studies on the neutralization of concrete specimens and the rusting of reinforcement embeded have been conducted throught 20 years.Kinds of cement used in this test were normal portland cement, blust furnace slag cement and portland pozzolan cement. The proportions of concrete of each kind of cements were as follows:Proportion Slump(cm) W/C(%) Compacted by1:2:4 {0 41-42 vibration5 50-51 rodding20 61-63 _??_1:3:6 {0 48-50 vibration5 68-69 rodding20 89-90 _??_Standard specimens of φ15cm×30cm with φ16mm steel bars, embedded were made in July, 1937, cured in moisture for 28 days, and then stored outdoors until the tests were mrde.The neutralization depth was measured by the use of phenol-phtalene alcohol solution on the splitted section of each specimen at the ages of 6 month, 1, 3, 5, 10 and 20 years, and at the same time, the rusting conditions of embedded steel bars were observed.The results of tests are summarized as follows:1) When concrete has not defects and the water cement ratio is smaller than 70%, the neutralization depth is less than 10mm and the neutralization scarcely pregresses further after it has advanced to certain depth. There results are same irrespective of kinds of cement.But, if concrete has some defects such as air voids, cracks and water film under aggregates, the neutralization develops mostly through the defects. Particularly when the water cement ratio is larger than 70%, for instance 89%, the neutralization progresses gradnally as the develops with age increases, and the neutralziation depth reaches 3-5 times as deep as that found in the concrete of smaller water cement ratio. In this case, the degree of neutralization varies depending upon the kind of cement; that is to say, concrete made with blended cement is neutralized much faster than concrete with portland cement.2) It is considered that the rusting of reinforcing steel occurs not by neutralization of concrete. Almost of the rusting of embedded steel bar develops due to the defects of the concrete, and movement of air or water through the defects.

Heats of hydration and pozzolan content of portland-pozzolan cements

Methods are described for the measurement of the approximate heat of solution in acid of portland-cement^-pozzolan mixtures. Examples are given of the estimation of the heat of hydration of portland-pozz olan cements. Determinations of the amount of material undissolved in the calorimeter, as well as the heats of solution, were applied to the problem of determining the composition of mixtures of portland cement and pozzolan. Data are presented for the calculation of the heat capacity of the vacuum-flask calorimeter with amounts of hydrofluoric acid other than the 8-milliliter quantity used in measuring the heat of hydration of portland cement by the standard method. 1. Introduction In recent years pozzolans have been widely used with portland cement because of their favorable effects on many of the properties of concrete. Many methods of test of cement or of concrete are not affected by the presence of the pozzolan, which contains a large percentage of silica. The measurement of the heat of hardening [1, 2] l of a portlandpozzolan cement by the heat-of-solution procedure however, is less reliable than the measurement for ordinary portland cement because of the presence of material not readily soluble in acid. The heat-ofsolution method depends on the measurement of the heats of solution in acid of a sample of dry cement and of a corresponding sample of hardened paste. The difference between the two heats of solution is the heat of hardening of the cement paste. A mixture of nitric and hydrofluoric acids, in which nearly all portland cements will dissolve rapidly and completely, is used. Considerable portions of many pozzolans, however, are not readily soluble, and for even approximately complete solution far more time would be required than is desirable in the usual procedure for portland cement. The Bureau has occasionally measured the approximate heat of solution or hydration of pozzolan cements in a variety of investigations scattered over a period of nearly two decades. This paper presents the results of tests made by methods devised to reduce the effect of the difficultly soluble material. In addition to the problem of measuring the heat of hydration of portland-pozzolan cements, there also exists, perhaps more urgently, the problem of determining the pozzolan content of such blends. In the course of the calorimetric measurements, it was observed that part of each pozzolan was undissolved. It was also observed that the heats of solution of the cement-pozzolan mixtures, as well as the percentage of undissolved material, were related to the pozzolan content. So that these data might not be lost, they have been included in this paper, and their application to the measurement of the pozzolan content of portland-pozzolan cements is discussed.

The Use of Portland-Pozzolan Cement by the Bureau of Reclamation

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