USE OF POZZOLAN IN REINFORCEMENT MORTAR FOR NON- STRUCTURAL MASONRY

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1 15 th International Brick and Block Masonry Conference Florianópolis Brazil 2012 USE OF POZZOLAN IN REINFORCEMENT MORTAR FOR NON- STRUCTURAL MASONRY Mota, João Manoel de Freitas 1 ; Oliveira, Romilde Almeida 2 1 MSc, Doctorate Student, Federal University of Pernambuco, Civil Engineering Department, joão@vieiramota.com.br 2 D.Sc., Permanent Professor, Federal University of Pernambuco, Graduate Program Civil Engineering, Professor, Catholic University of Pernambuco, Civil Engineering Department, romildealmeida@gmail.com In the metropolitan area of Recife (Brazil), the existence of several buildings known as caixão with up to four floors and built with non-structural block is perceived. These nonstructural masonries have been used for structural purposes and were designed without technological basis and relevant technical standards. The materials used, basically the blocks, do not have satisfactory performance. Several surveys were carried out in order to better understand the behavior of these buildings and establish a way of strengthening aiming at an adequate performance in service, and ensuring conditions for durability. It was verified that the mortar coating contributes to the hardness of the walls. This suggests the use of mortar with addition of pozzolan with steel as reinforcement, due to substantial increases in the mechanical properties and related durability. This study evaluates the influence of the metakaoline pozzolan in mortars through experimental studies. The mechanical properties and other related durability at 28 days and 90 days were evaluated. The results indicate that the addition of metakaoline mortars improves the properties studied. Keywords: non-structural masonry, reinforced mortar, pozzolan. INTRODUCTION In the Metropolitan Region of Recife-Brazil, masonry buildings were widely used since colonial times, due to the abundance of materials combined with the Portuguese culture regarding the use of ceramic masonry. From the 1970s, there was a great raise in the construction of affordable housing on a large scale. Buildings of up to four stories started to be built using blocks characterized as nonstructural blocks that nevertheless were used for a structural purpose. These constructions were executed in an empirical way without following specific technical standards and without any technical scientific basis to allow the establishment of acceptable structural reliability standards, which in turn resulted in the emergence of a number of pathologies and accidents. So far, 12 buildings have collapsed, resulting in 11 fatalities and many injured. In addition, a large number of buildings have been interdicted, for they do not provide safe conditions to their users.

2 It is known that these buildings were built without any technical basis and that materials and processes that did not meet structural requirements were used (MOTA, 2006). It is estimated that around caixão buildings, are in use in the Recife Metropolitan Region, housing approximately people (OLIVEIRA, 2004). These high numbers of buildings using non-structural masonry made of ceramic blocks with no structural function were conceived due to their low cost when compared to concrete buildings (OLIVEIRA; SOBRINHO, 2006). In addition, several pathologies were identified in these buildings so that about 160 buildings have been interdicted. Surveys of the buildings showed that the most loaded walls do not meet the safety requirements established by the relevant technical standards, mainly because the blocks do not meet strength requirements and resistance concerning to environmental agents. Nevertheless, buildings with over 30 years of existence are still in use (MOTA; OLIVEIRA, 2007). Generally, the most important cause of collapse of the so called caixão buildings was the brittle rupture of the foundation walls above the concrete slabs due to the deterioration of the foundation materials (OLIVEIRA, 2004). Figure 1 shows the generic scheme that well characterizes these buildings. In this context, reinforcement models for these buildings were developed by several researchers. Initially in Recife, Mota (2006) presented studies of prisms of ceramic blocks with the objective of analyzing the influence of coating mortar on stiffness. The author concluded that the best result (sample P6) increases axial compressive strength up to 322 in relation to the reference sample (P1), see Fig. 1. The identification of the samples are given as follows: P1 (reference single prisms); P2 (prisms with rough cast on both sides, ratio 1:3 cement and coarse sand); P3 (prisms with rough cast and plaster on both sides, the thickness of the coating of 2.0 cm and the use of a weak proportion 1:2:9, cement, lime and coarse sand); P4 (prisms with rough cast and coating on both sides, the thickness of the coating of 2.0 cm and the use of a medium proportion 1:1:6, cement, lime and coarse sand); P5 (prisms with rough cast and coating on both sides, the thickness of the coating of 3.0 cm and the use of a weak proportion) and P6 (prisms with roughcast and coating on both sides, the thickness of the coating of 3.0 cm and the use of a medium ratio). INCREASES IN AVERAGE VALUE () ,94 267,77 218,94 176, ,12 137, ,08 72, ,42 13,78 P2 P2 P3 P3 P4 P4 P5 P5 P6 P6 PRISMS SAMPLES Figure 1 Increase in resistance due to the influence of the coating 2

3 Oliveira et. al (2008) tested masonry prisms of ceramic blocks and non-structural concrete blocks used for structural purpose. Prisms with and without coating, and prisms with steel mesh embedded in the interior of the rendering mortar with and without connectors that interconnect the coating layers on both sides of the prisms were used. The authors obtained results on ceramic blocks prisms where the coating contributed to increase the load-bearing capacity of up to 335. Several types of rupture were identified. It was found that the rupture of the blocks occur due to the side traction in the horizontal partitions of the blocks, leading to unbalance in the state of confinements of the laying mortar. No significant load increases were observed when prisms with steel mesh without connectors were tested. In concrete blocks masonry prisms, an increase of up to 72 was observed due to the coating layer. However, the increase occurred at levels of up to 159 when steel mesh was used; the steel mesh equalizes the load distribution inside the coating with a subsequent influence on the rupture; when a double layer of reinforced mortar was used, the increase in load bearing achieved almost 300; the connectors increased axial load bearing capacity 65, prisms with 3.0 cm of reinforced coating with connectors increased the load bearing capacity 180. Pires Sobrinho et al (2009) tested 145 masonry small walls with the following characteristics: dimensions 0.09 m 0.60 m 1.20 m, hollow ceramic blocks with eight holes (dimensions: cm each), a mixture of cement, lime and sand mortar with a volumetric mixture ratio of 1:1:6. In this study, it was concluded that the mortar coating increases the stiffness of the walls proportionally to the thickness and to the elasticity modulus of the mortar; the coating does not change the rupture pattern of the masonry, which occurs in a brittle mode. However, it was found that the coating does have an effective participation in the compressive behavior of the walls; the steel mesh reinforcement, with the locking of the reinforcement inside the coating, increases the load bearing capacity of the walls, and, basically, produces significant change in the rupture pattern, leading to a plastic behavior, below the rupture level, allowing for a redistribution of strains and deformations between the elements of a structure. Therefore, nowadays a reinforcement model suitable for the use of reinforced mortar with the addition of pozzolan is being researched in order to increase mechanical properties, as well as those related to durability, thus this can be one of the reinforcement models recommended for constructions with these characteristics i.e., buildings with resistant masonry (walls with nonstructural ceramic blocks). In this case, the refinement of the pores in materials with a cementitious matrix, provides a greater barrier to the reinforcement inside the mortar, preventing: sulfate attack, salt spray (chloride ions), carbon dioxide, and humidity among other aggressive agents increasing as well the mechanical resistance (MOTA; OLIVEIRA; DOURADO, 2011). Neville (1997) states that the pozzolans added to the mortars and concretes, promote a higher density of the mix generating a natural porosity reduction from the interface to the surface (due to the wall effect). Galvão (2004) observed that mortars with addition of metakaolin considerably increased mechanical properties when compared to mixed mortars with no metakaolin. It is known that, in a number of cases, mortars with metakaolin exceeded in terms of bonding properties. 3

4 It was concluded that in research with pozzolan, the addition of this material to mortars tends to increase mechanical performance up to 2.75 times, especially in bonding strength of inorganic mortars (TAHA, 2001). Figure 2 shows the metakaolin positioned between the cement particles, filling the gaps (physical effect filler) and reacting with the calcium hydroxide turning into C-S-H (chemical effect). This physical phenomenon explains the decrease of gaps, for it takes place before the pozzolanic reactions start, when the finer inert metakaolin particles fill the existing spaces that would otherwise be occupied by air. Figure 2 Metakaolin Electronic Microscopy magnified 3000 X (Source: Figure 3 shows pozzolan particles in the cement interstitial spaces. Figure 3 Metakaolin pozzolan particles in the cement interstices (Source: Figures 4A and 4B show the electronic microscopy of the region located between the reference paste with pure cement (left) and the paste with an 8 metakaolin content (right) replacing cement, both at 28 days. The darker regions represent porosities or interstices. A B Figure 4 Metakaolin pozzolan particles in the cement interstices (Source: 4

5 This study aims to evaluate the increase in mechanical properties of reinforced mortar with addition of metakaolin. METHODOLOGY AND MATERIALS The study was conducted on four samples of mortar mix consisting of cement, hydrated lime and sand, with percentages of 0, 10, 15 and 20 addition of metakaolin in relation to the cement volume. Cylindrical specimens were prepared for each case in order to investigate mechanical properties (axial compressive strength, traction by diametral compression and tensile bond strength). All studies were performed at the Civil Engineering Laboratory (LEC), of Vale do Ipojuca College FAVIP (Caruaru, Pernambuco), which is part of the developed research. During the preparation of the samples, mortar workability was kept constant, measured from the flow table at a value of 200 mm + 20 mm. The quantities of materials used are listed below: sample 1 (reference - 0 metakaolin) 1:1:6:1.5 (cement:lime:sand:water/cement ratio); sample 2 (10 metakaolin replacing cement) 1:1:6:1.5; sample 3 (15 metakaolin replacing cement) 1:1:6:1.5; sample 4 (20 metakaolin replacing cement) 1:1:6:1.5. To evaluate the influence of metakaolin on the mechanical performance of the mortars, tests were performed at 28 and 90 days, using the same amount of samples in both cases. 15 replicas per sample for each age 28 days and 90 days, were used. For all tested specimens, cylinder surfaces were capped with sulfur on both sides. The tensile bond strength test was accomplished by cutting the mortar into a 10 cm 10 cm square shape. After bonding the metal plates with epoxy, rupture of the sample was carried out after 24 hours. Both sides of the wall were used for the test, one with conventional roughcast in a 1:3 ratio (cement and sand) and the other side with roughcast with replacement of 5 metakaolin. Statistical analysis was performed by calculating the standard deviation of all results, eliminating values more than three times the standard deviation away from the mean, for each side. Afterwards, a new mean value, standard deviation and variation coefficient were calculated, according to the table. MATERIALS Binders - CP II-F-32 cement and CH-II hydrated lime were used, both are widely used in the region; Additions The metakaolin used is industrialized in the Recife Metropolitan Region, originating from high reactivity kaulinitic clay, with the following basic characteristics (informed by manufacturer): White color; specific mass density 2.49 g/cm 3 and apparent mass density 0.43 g/cm 3 ; 5

6 Fine aggregates Natural quartz sand widely found in the region of the city of Caruaru (PE), was used. This material is characterized by specific and apparent mass density, and determination of the granulometric curve and coefficient of uniformity according to the Allen- Hazem method. This method relates C = d 60 /d 10, meaning the equivalence of percent passing of material. Table 1 shows the features of the natural sand. Table 1 Features of the sand used in the research Maximum characteristic dimension 2.36 Fineness module 2.15 Apparent density (g/cm³) 1.63 Specific mass (g/cm³) 2.56 Uniformity coefficient 1.20 Blocks: The masonry base executed with non-structural ceramic blocks was built next to the laboratory and had the following features: average length, height and width measurements (19.0 cm; 9.5cm and 19.1cm); mass g; IRA (Initial Rate Absorption) 12.2 g/200 cm 2 /min and total absorption 12.3 ; Water: The water used came from the water supply system of the Pernambuco Sanitation Company (COMPESA). It was verified that the ph of the water used, was close to 6.5. RESULTS AND DISCUSSIONS The results of mechanical tests regarding compressive strength are presented on Table 2. Table 2 Results of compressive strength tests AXIAL COMPRESSIVE STRENGTH (MPa) Samples Age in days Avg SD Avg SD Avg SD Avg SD Figure 5 shows the rupture mode of the specimens. 6

7 Figure 5 Specimen during the compressive strength test An increase in compressive strength in the samples with addition of metakaolin was observed when compared to the reference sample and in relation to time, as well. In regards to traction by diametral compression, Table 3 presents the results of the tests performed. Table 3 Results of traction by diametral compression TRACTION BY DIAMETRAL COMPRESSION (MPa) Samples Age in days Avg SD Avg SD Avg SD Avg SD Figure 6 shows a specimen during traction by diametral compression test. Figure 6 Traction test by diametral compression test 7

8 Satisfactory results were also observed for the tensile strength test, considering the increase for the samples with metakaolin in relation to the reference sample. There was also an increase in the results when compared the 28-days age with 90-days age. Table 4 presents the results for the tensile bond strength test. Age in days WITHOUT ADDITION PREDOMINANT RUPTURE WITH ADDITION RUPTURE Avg Table 4- Results of tensile bond strength test Samples SD Avg SD Avg SD Avg SD ROUGH CAST/BLOCK /BLOCK /BLOCK BLOCK AND BLOCK AND MORTAR /BLOCK It was observed that there was an increase in tensile bond strength as pozzolan was added. It was also found that bonding increased at 90-day age when compared to 28-day age. Figures 6a and 6b show the test in loco. A Figure 7 Tensile bond strength test B 8

9 CONCLUSIONS - It was observed that axial compressive strength of the mortars increased as of addition of pozzolan increased, and in relation to time, as well. The largest increase was in sample 4 at 90 days in relation to the reference sample at 28 days (69.9), thus evidencing the effect of pozzolanic reactions; - The tensile bond strength by axial compression, with the addition of metakaolin increased in relation to time. The greatest increase occurred in sample 4 at 90 days in relation to sample 1 at 28 days (155); - Concerning to tensile bond strength, it increased when the extraction in the reference sample was compared to samples with addition, as well as to the side where the rough cast had pozzolan addition. The most significant increase achieved 53.5; - This study indicated that the addition of pozzolan in mortars contributes to the improvement of mechanical properties, an important fact for the entire universe of mortars, and, significantly, for the reinforcement of mortars. REFERENCES GALVÃO, S. P. Performance evaluation of structural repairs mortars based on Portland cement modified by polymers and containing mineral additions (in portuguese). Master Thesis (UFG), MOTA, J. M. F. Influence of Coating Mortar on Axial Compressive Strength of Resistant Ceramic Blocks Masonry Prisms (in portuguese) Master Thesis. UFPE Federal University of Pernambuco. Recife, PE. MOTA, J. M. F.; OLIVEIRA, R. A. Rupture forms in resistant ceramic blocks masonry prisms (in portuguese). II Brazilian Congress of Bridges and Structures, Rio de Janeiro, Mota, J. M.F ; Oliveira, R. A; Dourado, K. C.A. The use of pozzolan in reinforcement mortars for resistant masonry (in portuguese) 7th International Congress on Pathology and Rehabilitation of Structures. Fortaleza, NEVILLE, A. M. Properties of concrete (in portuguese). 2. ed. PINI. São Paulo, OLIVEIRA, R. A. Class Notes from the Structural Masonry Subject Master of Structures (in portuguese), UFPE Federal University of Pernambuco, Recife, OLIVEIRA, R. A.; SILVA, F. A. N.; PIRES SOBRINHO, C. W. Buildings constructed with resistant masonry in Pernambuco Current situation and future outlook (in portuguese) In: Bernardo Silva Monteiro; José Afonso Pereira Vitório. (Org.). O Sinaenco-PE and the production of knowledge. 1a ed. Recife: Sinaenco, 2008, v. 1, p OLIVEIRA, R. A. e PIRES SOBRINHO, C. W. A. Accidents with buildings constructed with resistant masonry in the Recife metropolitan region (in portuguese). DAMSTRUC, João Pessoa PB,

10 OLIVEIRA, R. A.; SILVA, F. A. N. ; SANTOS, L. V. ; AZEVÊDO, A. C. Compressive Behavior of Ceramic Sealing Blocks and Concrete Prisms with and without the Addition of Resistant Mortar (in portuguese). Symposium (Recife), v. 12, p. 5-27, PIRES SOBRINHO, C. W.; OLIVEIRA, R. A.; SILVA, F. A. N.; ANDRADE, S. T. Influence of simple and reinforced coating on the behavior of resistant ceramic blocks masonry small walls (in portuguese). In: 5 o. CINPAR International Congress on Pathology and Rehabilitation of Structures. Curitiba, TAHA, M. M. R.; SHRIVE, N. G. The use of pozollans to improve bond and bond strength. 9 th Canadian Masonry Symposium. Canadá,