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Revista ingeniería de construcción

versão On-line ISSN 0718-5073

Rev. ing. constr. v.24 n.2 Santiago ago. 2009

http://dx.doi.org/10.4067/S0718-50732009000200005 

Revista Ingeniería de Construcción Vol. 24 N°2, Agosto de 2009 www.ing.puc.cl/ric PAG. 181- 194

 

Effect of lime- zeolite binder on compression strength and durability properties of concrete

 

Juan José Dopico Montes de Oca**, José Fernando Martirena Hernandez*, Alberto López Rodríguez**, Raúl González López*

* Universidad Central Marta Abreu de las Villas. CUBA

** Empresa Prefabricado Industrial Villa Clara. CUBA

Corresponding author:


ABSTRACT

The international construction practice reports a remarkable use and development of high performance concretes, with excellent results in the durability properties, associated with a very dense cement matrix, defined from the use of high volumes of very fine minerals additions, such as, fly ash, silica fume, metakaolin and other fine powders. For the developing countries, among others Cuba, the use of these pozzolanic additions are relatively expensive, given for the high import prices of these pozzolanic materials, thus, the utility of using the national available pozzolanic sources with proven reactivity, as a partial substitute of the Ordinary Portland Cement (OPC) contents in the concrete mixtures without its properties are affected. The present paper shows the results of the study on the influence of substitution level of Ordinary Portland Cement contents by lime - pozzolan binder in combination with chemical admixture, in the behavior of the compression strength and the durability properties of a concrete. Several levels of OPC substitution are evaluated, using zeolite as pozzolan. The results obtained prove the possibility to carry out the partial replacement of high volumes of OPC by lime - zeolite binder, without affecting the values of compression strength required and their behavior before action of the chloride ion penetration and the carbonation.

Keywords: Supplementary cementitius materials; compression strength; lime - pozzolan binder; chloride ion; carbonatation; zeolite


 

1. Introduction

The incidence of Ordinary Portland Cement (OPC) production emissions in global warming, the continuous and increasing interventions for repairing and reconstructing concrete structures, as well as the result of wrong designs, deficient construction and insufficient maintenance programs, call the attention of specialists and governments, in relation to the compelling subject of buildings service life; this results in an expensive process, not only from the economic but also from the ecological point of view Aitcin (2000); Bentur and Mitchel (2008).

The necessary measures that should be taken in order to essentially decrease the aggressiveness towards the environment during cement production should consider the improvement of the process efficiency, minimizing mineral fuels consumptions and increasing the use of clinker expanders, such as supplementary cementing materials (SCM's). The use of SCM's, added during the Portland cement production or during the concrete production process, has demonstrated not only to be effective in reducing emissions but also to improve mixtures rheological characteristics, to decrease the hydration temperature and porosity, to improve mechanic strength, even with strong reductions in the Portland cement content, as well as to improve reinforced concrete durability of structures Martirena (2004); Scrivener and Kirkpatrick, 2008)

Pozzolan additions are used as SCM, provided that the pozzolan is reactive. The contribution of pozzolanic reaction products is associated with: the amount of Ca(OH)2 produced during the cement hydration reaction, the material fineness, as well as the type and period of curing during the first ages. For OPC substitutions in mass by approximately the 50% or more, the main contribution of the pozzolanic material is better verified as inert filler, than if high fineness pozzolan is added to the concrete mass together with the calcium hydroxide (lime-pozzolan addition), the lime addition to the fresh mixture would contribute to a reaction of greater amount of pozzolan, so the potential of the reaction products may be increased (Mira et al.,2001; Martirena, 2004).

Moreover, the additional calcium hydroxide presence would increase the concentration of Ca 2+ and OH ions in the solution and, with this, it would accelerate the starting of the pozzolanic reaction from the beginning. From other point of view, the employment of pozzolan mixed with lime, of similar fineness to that of the OPC, will reduce the risk of concrete decalcification, even for large substitution volumes, starting by the pH rising of the water contained in pores, which would prevent the reinforcement passive protection. (Mira et al., 2001; Sebaibi et al., 2004; Brouwers and Radix, 2005; Shi et al., 2005; and Jatuphon et al., 2005). Similarly, the lime-pozzolan mineral addition will contribute to complement the fines grading distribution; in this manner, the calcium hydroxide is able to fill the voids among cement grains and, eventually, the highly fine pozzolan may fill the very small spaces present among the small grains of the fine aggregate. This principle is applied to the mix design of self-compacting concretes and high strength concretes, obtaining excellent results in mechanics properties and durability, in addition to remarkably reduce the consumption index of the OPC (Bornemann, 2002; Martirena, 2004; Jatuphon et al., 2005).

This paper shows the influence of replacement of OPC contents by a lime-pozzolan mineral addition, combined with superplasticizer, on fresh concrete behavior, compressive strength, and durability of concrete. This is evaluated at different replacement levels, until reaching the maximum possible replacement level of OPC by the addition of lime-zeolite (LZA), without significantly affecting the concrete compressive strength, the chloride ion penetration and the carbonation phenomenon.

2. Development and discussion

2.1. Materials

The Portland cement responds to the denomination P- 350 (Type I), manufactured by the Carlos Marx Cement Plant, in the Province of Cienfuegos. Table 2.1 shows the main characteristics of this type of cement.

Table 2.1 Cement Physical Tests

 

The physical tests results show the cement specifications compliance with Cuban standard NC 95 / 200Ion Portland Cement. Specifications.

Calcium hydroxide (Lime) is sold in 22 kg paper bags, manufactured by Empresa Azucarera Pepito Tey, Cienfuegos. During the tests period, these bags were protected with plastic bags in order to limit carbonation. Calcium hydroxide specific weight was 2.46, with a Blaine specific surface of 7656 cm2/g and a 72% content of reactive lime.

A zeolitic tufa was used as pozzolan source, which was obtained during the milling process, in La Tasajera Plant, Ranchuelo; it is named Zeomicro and has a specific weight of 2.29. Table 2.2 shows lime and zeolitic tufa chemical compositions, which were obtained by X-rays fluorescence spectrometer.

Table 2.2 Lime and Zeolite Chemical Composition

According to ASTM C 618- 03, the pozzolan used classifies as pozzolan type F, since it contains more than a 70% of the main oxides Si02 + Fe203 + A1203. Figure 2.1 shows the grading behaviour of the cementitious materials used.

Figure 2.1 Grading Distributions of Each Binder Summatory (Laser Particles Size Analyser Malvern Mastersizer)

The coarse and fine aggregates used come from crushed limestone rocks, obtained in the "Mariano Pérez" Pit, in El Purio. The chemical composition shows a CaC03 content over 90%, and Si02 content less than 5%. As coarse aggregate, a stone of maximum size 9.72 mm, with a fraction of (10-5) mm (Granite) was employed. Aggregates physical characteristics of are detailed in Tables 2.3 and 2.4.

Table 2.3 Physical Characteristics of Aggregates

Table 2.4 Grading Distribution of Aggregates

The physical tests indicate that aggregates specifications comply with the Cuban standard NC-251/2005, on Aggregates for Hydraulic Concretes, Requirements.

MAPEFLUID N200 was used as chemical admixture. It is a superplaticizer of moderate retarding action, water reducing admixture, Type F according to ASTM C 494. Consumption (0.5-1.5)% of cement weight (0.4- 1.25) 1, 1.2 of Specific Weight.

2.2 Experimental Plan

In order to evaluate the influence of lime-zeolite mineral addition in the compressive strength behaviour and durability of a concrete, the following experimental program was executed, based on the employment of the proposed idea of correcting the mixtures composition using mineral additions (Martirena, 2004), as follows:.

1. Concrete Control Mix proportioning, with superplasticizer and without mineral addition, using the O'Reilly design method of proportioning mixtures, employing available raw materials and the required properties for fresh concrete, specifying the appropriate consistency and workability, according to the technology used and the strength parameters required at 28 days, O'Reilly, (1990). Experimental determination of fine aggregate proportioning: coarse aggregate and superplasticizer proportioning, starting from the flow test in pastes using the Marsh Cone Test, according to NC- 461/2006 on Flow Determination of Portland Cement Grout Using the Marsh Cone, Step I.

2. Experimental mixtures manufacturing, for different mass replacement values, where the amount of OPC defined in the Control Mix is gradually replaced by a similar mass of the Lime-Zeolite Addition (LZA) and water is added until obtaining the required consistency. The substitution limit of OPC/LZA is established from the analysis of the compressive strength values obtained, and with them the paste volume determination (Vpaste), Step II.

3.  Manufacturing of experimental mixture for different substitution levels β) in OPC/LZA volume, where the amount of OPC is changed in volume by LZA, maintaining Vpaste constant. OPC/LZA limit determination from evaluation of concrete compressive strength values, Step III.

4. Practice of durability tests in experimental mixtures of Step III. OPC/ LZA Substitution Limit Determination starting from the evaluation of durability criteria.

Experimental mixtures prepared for similar workability, using a gravitational concrete mixer of 150 litres capacity, and a mixture proportioning of 47% sand, 53% stones and 1.2 % of superplasticizer. Cylinder specimens of 300 mm x 150mm were used for compressive strength tests and cylinder specimens of 200 mm. x 100 mm. were used for durability tests. Specimens were water-cured until tested. Specimens for durability tests were exposed to environment, after 60 days of curing. The paste volume was calculated considering the volumes proportioned, in each mixture, by the cement, lime, zeolite, water and superplasticizer.

2.2.1 Control Mix

The Control Mix, without mineral addition and with the MAPEFLUID N200 superplasticizer, was designed to obtain a compressive strength of 30.0 MPa at 28 days, w/c ratio of 0.4, two percent of air content and 12± 1 cm. of slump measured by the slump test, to be used in the manufacturing of concrete elements, that required a 9.52 mm maximum size of the coarse aggregate. Table 2.5 shows the mixture design used.

Table 2.5 Control Mix Proportioning

In Figure 2.2 it can be appreciated that the control mix design fulfills the compressive strength requirements at 28 days, as it was designed.

2.2.2. Manufacturing of Experimental Mixture. Step II

The experimental mixtures concerning this step were obtained from the Control Mix variation, the amount of OPC by lime-zeolite mineral addition (LZA), the evaluation of levels 10%, 20%, 30% and 40% of mass substitution and maintaining constant the rest of the constituents. Water was controlled until obtaining slump values of 12+1 cm measured by the slump test. The addition of the constituents of the mineral addition was done independently, in proportion of 20% lime and 80% zeolite in mass. Compressive strength at 3, 7, 28 and 60 days of each mixture was measured.

The OPC/LZA substitution limit and the paste volume (Vpaste) that will be used in Step III, will be defined by the experimental mixture, whose substitution level offers compressive strength values at 28 days that is not significantly different from the one defined by the Control Mix. In this way, the concrete mixture proportioning and characteristics were obtained, as well as the results of the mean compressive strength, as shown in Table 2.6 and Figure 2.2.

Table 2.6. Experimental OPC/LZA Mixture Characteristics (Substitution in mass)

The use of lime-zeolite mineral addition produces an effect on the characteristics of fresh concrete. As it can be seen on Table 2.6, and considering as a reference the Control Mix, the paste volumes increases as the substitution level of the OPC by LZA increases, except for the 10%, and in all cases, the paste volume exceeds the voids volume among aggregates of 263.8 liters. These increments of the Vpaste are related to the increase of mixture water demand and with the differences of density between the addition and the cement.

The paste volume increase in the mixture causes separation among the aggregates, thus decreasing friction among them and, as a consequence, the rheological characteristics (plasticity, fluidity) of the mixture experienced few changes as well as water consumption, similarly as with self-compacting concretes.

The paste volume decreasing in the mixture of 10% of substitution is associated to the combined action of the LZA and the superplastificizer, obtaining the required workability for a minimum demand of water. Working with a constant amount of superplasticizer in the mixture, causes the dispersion effect to have a greater action in the mixture with 10% less of cement, plus the plasticizing effect of the addition, mainly contributed by lime. The effects on the lime-zeolite mineral addition compaction would justify the increments on the early ages strengths.

From the results showed in Figure 2.2, the influence of the OPC replacement level by LZA by mass over compressive strength can appreciated. Over the 30% of LZA replacement by mass, compressive strength decreases strongly for all the ages. The preceding fact is given by the decrease in the reaction products contribution, which contributes to the matrix strength, mainly of the OPC.

When comparing the mean compressive strength values among mixtures, it can be observed that there are no great differences at ages of 28 and 60 days between the Control Mix and the 30% of substitution in mass; this difference is important for the rest of the comparisons. Thus, this mixture defines the substitution limit in mass for OPC by LZA, with Vpaste equal to 295.73 litres.

Figure 2.2 Compressive Mean Strength Behaviour According to the Substitution Level of OPC by LZA in Mass

2.2.3. Manufacturing of Experimental Mixtures. Step III

In order to determine the substitution limit in volume of OPC/LZA at this step, the OPC and LZA proportioning were varied in volume β) within the paste volume that defines the mix with a 30% of substitution by mass. In turn, this mixture is defined as the mix of 37% of substitution in volume, which henceforth will be called β-40. If the paste volume, aggregates, water and the amount of superplasticizer are maintained constant, in such a way that the water/fines ratio in volume is kept constant, the OPC and LZA proportioning in volume are varied, and the points that correspond to the 20% β(-20) and the 60% β-60) of substitution in volume are evaluated as experimental mixtures, prepared in similar conditions to the preceding step mixtures. In this way, the proportioning (expressed in mass units) and mean compressive strength results were obtained, as can be seen in Table 2.7 and Figure 2.3.

Table 2.7 OPC/LZA Experimental Mixture Proportioning (Substitution in volume)

Figure 2.3 Mean Compressive Strength at Different Ages

In this step, the experimental mixtures prepared with similar volumes of paste and a constant water/fines ratio, maintain their rheological characteristics of plasticity and fluidity with few changes, and are measured by the similarity in the slump values obtained.

Variations in the substitution levels of OPC by LZA in volume β3), within a constant paste volume, also carry out a variation on the strength values obtained, increasing or decreasing, depending on the OPC volumes present in the respective mixtures, as it can be appreciated in Figure 2.3. Authors consider that the preceding is given by the contribution of each binder on solids production, mainly for those shared out in the OPC hydration, and the differences in the mean compressive strength when compared with the results among mixtures are significant.

From the analysis of the mean compressive strength obtained, it is considered that using up a 37% of substitution in volume of OPC by lime-zeolite addition, it is possible to guarantee the required strength values denned by the Control Mix.

2.2.4. Durability Analysis

When evaluating the behavior of concrete mixture durability in Step III, including the Control Mix, the results obtained in the Rapid Chloride Permeability Test (RCPT) are evaluated according to the ASTM 1202 "Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration" and carbonation depth determination according to the NC 355/2004 Carbonation Depth Determination on Hardened Concrete put In Service.

2.2.4.1 Chloride Ion Penetration Resistance

In the RCPT (see Figure 2.4), the charge passed is determined in Coulombs during 6 hours, in one year old samples. In function of the charge passed in Coulombs, normalization evaluates the chloride ion penetration resistance in: High (> 4000), Moderate (2000 - 4000), Low (1000 - 2000), Very low (100 - 1000) and Insignificant (< 100). The results obtained are showed in Figure 2.5.

Figure 2.4 Set for Quick Test of Chloride Ion Migration, according to AAHSTO T277(left); Set used by the author (right).

 

Figure 2.5 Charge Passed in Coulombs at 1 Year. Results of the Charge Passed by Hour (left); After 6 Hours (right)

When analyzing concrete resistance against chloride ion penetration, according to the parameters established by the ASTM C1202, a moderate penetrability for all the mixture is obtained.

In the results showed by Figure 2.5, an increase in chloride ion permeability, as replacement level of OPC by LZA increased, can be observed. Nevertheless, when comparing the mean values of the charge passed, between levels β-20 and β-40, and of these with the Control Mix, it does not exist a significant difference in the mixture resistance against chloride ion penetration. This might be given by the changes in the connectivity of the capillary porous network in the concrete matrix as a consequence of hydration reactions, given by the mineral addition, being the effect slightly higher with the 20% of substitution.

The mixture with 60% replacement level shows higher values of chloride ion permeability. In this mixture, it can be assumed that the presence of higher amounts of unreacted additions may influence their high absorption power in decreasing the electric power pass resistance through the sample.

These results allow to confirm, that when working with the mixture within the selected paste volume as a constant, up to 37% β-40) of substitution in volume of OPC by LZA, the resistance against chloride ion penetration, results similar to that offered by the Control Mix; over this substitution value, steel reinforcement corrosion may appear earlier than for the rest of the evaluated mixtures.

2.2.4.2. Carbonation depth

Considering that carbonation is a long process through time, the atmospheric C02 was evaluated in samples at the ages of 2 years. The results obtained in the measurement of C02 penetration test through the surface coloration changes of samples by the phenolphthalein spray method are shown in Table 2.8 and Figure 2.6

Table 2.8 Penetration of Atmospheric CO2

 

The Control Mix, compared with the results from the mixture with additions, presents the lower penetration values facing the action of the atmospheric C02. The mineral addition affects carbonation front formation, since the later increases with the increase on the substitution levels of OPC by LZA. Nevertheless, when comparing the penetration mean values defined between levels 6-20 and 0-40, and of these with the Control Mix, there are no significant differences defined among the values obtained. The higher penetration obtained in0- 60 may be given by the presence of greater amounts of calcium hydroxide in the addition, that possibly may react to create the carbonation front.

Figure 2.6 Progress of Carbonation Front, a) Control Mix; b£-20; c) K-40 y d) ft-60

The preceding results confirm that, when working the mixtures within the chosen paste volume as a constant, up to 37% β-40) of substitution in volume of OPC by LZA, the behavior facing the atmospheric C02 penetration results similar to that offered by the Control Mix. Over this substitution value, the steel reinforcement depassivation and with it, corrosion, may appear earlier than for the rest of the evaluated mixtures.

From the analysis of the results of this final step, the mixture with 37% of substitution in volume of OPC by LZA, not only reached the compressive strength requirements but it also it gave satisfactory results facing the aggressive agents action.

3. Conclusions

1.  The results obtained show the influence of the LZA and that of the substitution level in volume of OPC used, in the behavior of the compressive strength and durability. These changes mainly agree with the effective action of the mineral addition in the contribution of hydrated products, in the compaction improvement and in the decrease of the porosity associated to the interconnected capillary pores.

2. The use up to a 37% of substitution in volume of OPC by LZA in combination with MAPEFLUID N200, within a constant paste volume, does not only satisfy the compressive strength requirements and workability demands, but it also obtains satisfactory results in durability, with good reductions in cement consumption and without affecting the requirements of the Control Mix.

3.  When evaluating different mixtures with similar constituents and paste volume, it is necessary to consider the required interval for the amount of Portland cement necessary to obtain a given concrete, in agreement with its application and structural strength, using a lime-zeolite addition, obtained from the zeolitic tufas extracted during the industrial production.

4. References

 

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ASTM C 618- 03. (2003), Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete. 2003, ASTM         [ Links ]

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