Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 193 (2017) 198 – 204
International Conference on Analytical Models and New Concepts in Concrete and Masonry Structures AMCM’2017
The role of mortar microstructure in providing the face wall structural integrity Maria Wesoáowskaa,* a
University of Science and Technology in Bydgoszcz, Department of Building and Building Physics, Kaliskiego 7, 85-796 Bydgoszcz, Poland.
Abstract The basic condition for proper function of a face wall in external environment is providing structural integrity within its entire period of usage. Structural integrity can be defined as construction ability to maintain bearing capacity, functionality and shape within acceptable ranges without arising state of emergency during exploitation. Wall structural integrity results first of all from construction mortar which, except for bearing function should also provide protection from entering water into the wall interior. The processes of water capillarity, drying, and freezing are dependent on microstructure and open porosity. In the article there are introduced tests of three mortars (cement, cement with plasticizer, and cement-lime based) formed in wall joints. In order to prepare mortar samples from joints of wall elements for porosimetry tests, mortar was separated from bricks in such way that whole joint was left intact. By breaking, each layer of mortar was divided parallel to the joint surface into three parts – two parts adjacent to brick base (each 1/4 of layer thickness) and the middle part sized 1/2 of joint thickness. By Mercury Intrusion Porosimetry the basic microstructure parameters were measured, as well as pore volume distribution in the function of their diameters as integral and differential relation. The analysis of pore volume variation for integral distribution let us state the pore sizes which as additional, are formed in mortar in the area of joint adjacent to wall element surface. Independently of mortar type, in this area there are additional pores created, which are responsible for capillary flow. In cement mortars there are additionally macropores created which decides about water migration through a joint and about its gas permeability. © Authors. Published by Elsevier Ltd. This ©2017 2017The The Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility ofthe scientific committee of the International Conference on Analytical Models and New Peer-review responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in Concepts inunder Concrete and Masonry Structures.
Concrete and Masonry Structures
Keywords: microstructure; mercury intrusion porosimetry; masonry mortar
* Corresponding author. Tel.: +48 52 340-86-79. E-mail address:
[email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International Conference on Analytical Models and New Concepts in Concrete and Masonry Structures
doi:10.1016/j.proeng.2017.06.204
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1. Introduction The basic condition for proper functioning of walls is maintenance of structural integrity throughout the entire period of usage. This feature is largely discussed in the context of wall strength to static and dynamic loads as well as in ensuring proper work conditions of historical buildings [1,2]. Arandigoyen et al. [3] wrote that for maintenance of wall continuity the choice of mortar is essential. In this case a special role is fulfilled by lime, which affects mortar plasticity and ability to absorb strains resulting from wall movements. Researches led on lime-based mortars in historical buildings indicated that this binder causes proper lime placement in the joint and favorable shaping of microstructure [4]. Mechanical and rheological features of mortar are shaped by all components. Besides binders, aggregate has significant influence [5], but also eventual additions. Special role is played by plasticizers. They are additions which basic application is to modify features of concrete mixture and concrete. However, numerous researchers claim that they can be effectively used for cement mortars [6]. According to Kamouna et al. [7] a plasticizer can reduce water content, improve mortar workability and compressing strength. It allows also slower pace of cement mortar workability decrease [8]. But masonry mortar should be adjusted to both a wall element and joint [9]. Its main task is to provide homogeneity in contact area of a wall unit and mortar. The mortar used should protect against water entering into wall interior and enable to let it outside (e.g. after intensive long lasting rain). The choice of mortar should take into account its service function toward wall elements. Kubica et al. claim that mortar should be a link for a wall element, and elastic bed. Loss of wall integrity is caused first of all by inappropriate choice of mortar [10]. Traditional macroscopic tests do not allow exact prediction of clinker behaviour in contact with mortars and external environment. Processes of capillary rise, freezing and drying are tightly associated with microstructure and open porosity. Due to limited permeability and capillarity of present clinker elements the meaning of mortar microstructure formed in joint is increasing. 2. Research methods The tests were performed on a group of three masonry mortars: cement, cement with plasticizer, and cementlime with contents described in Table 1. The basic goal of research was a comparative evaluation of formed mortar microstructure changes in: - Standard beams sized 40x40x160mm, cured for 28 days in standard conditions, - In a joint of connected samples, made of two clinker bricks joined with masonry mortar 1cm thick, cured for 28 days in standard conditions. Table 1. Composition of tested mortars Mortar contents (volume) Mortar
Cement CEM I 42.5N
Lime
Sand
Plasticizer [g/kg cement mass]
Cement mortar 1
1
-
3.5
-
Cement mortar 2
1
-
3.5
0.32
Cement-lime mortar
1
1.25
6.75
-
For the particular three types of mortar there were formed two kinds of samples, each including six standard beams and connected samples. After the curing period the beams were dried to solid mass for 72h in temperature of +105±5°C. Then samples were taken out from the drier, they were cooled in an exsiccator and weighed after the temperature was from 30 °C to 40 °C. Next they were measured and mortar volume density was defined (ȡob). Then mortars from central part of beams were taken, and they were combined into general sample which was again dried to solid mass. From the general sample there were three random elements taken which served for measuring density (ȡ) by a pycnometer. The rest of the sample was put again into the drier 40°C to maintain drying effect.
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Fig. 1. Extraction of samples from connected sample joint
Microstructure tests were performed with the AutoPore IV porosimeter 9500 series equipped with two ports: low and high pressure of 33000 psia (228MPa) maximum value. This particular range enables measuring of pore volume and size distribution within the range from about 7000 nm to 3 nm. This test requires nearly complete filling of the penemometer bulb, and estimated pore volume should be within 90% to 25% of measuring capillary volume. One size of penemometer bulb and capillary was set which was applied to all mortars (both for these which were formed into beams as well as those originating from the joint). Confirmation of correct penemometer size were measurement results indicating values of about 60%. In order to prepare mortar samples to porosimetry tests, mortar was separated from the brick so that whole joint was left intact. By breaking, each mortar plaster was divided parallel to joint surface into three parts – two parts adjacent to brick base (each 1/4 of plaster thickness) and central part sized 1/2 of plaster thickness (Fig.1). From such prepared general samples there were selected laboratory samples marked: C (central joint part) B (side joint parts). Then samples were dried to solid mass for 72h in temperature of +105±5°C and cooled to 40°C in an exsiccator. Directly before the porosimetry test, samples were weighed with tolerance of 0.001g and put in penetrometer, installed in a low pressure port. Resulting from mercury porosimeter measurements, the following microstructure parameters were defined: total pore volume, sample volume and real density of material skeleton, pore volume distribution in function of their diameter as integral and differential relations. Capillary flow takes place in pores with diameters within the range of 3.0 x 10-7 ÷ 3.0 x 10-6 m (300 ÷ 3000 nm). The volume share of these pores was calculated according to the formula (1): 3000nm
U cap
¦ =
i =300nm
TIV
IVcap
⋅P
(1)
where: IVcap - mercury intrusion within diameter the range of 300÷3000 nm, TIV - total mercury intrusion, P – general porosity, % Pores with smaller diameters because of essential influence of friction forces, and pores with bigger diameters because of essential influence of gravitation forces determine capillary flow in much less degree. 3. Results and discussion The measurements of open pore amount and sizes on mortar samples taken from beams indicated that cement 1 mortar is characterized with low porosity shaped with pores of big diameters (1ǜ103 nm). Plasticizer addition (cement 2 mortar) caused visible increase of porosity (Tab. 1), in which dominant diameters are 1ǜ103 nm and 0.09ǜ103 nm. Samples of cement-lime mortar have porosity close to mortar with plasticizer, but porosity distribution is bimodal with dominant diameters 0.3ǜ103 nm and 70ǜ103 nm.
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Maria Wesołowska / Procedia Engineering 193 (2017) 198 – 204 Table 2. Tested mortars microstructure parameters Mortar samples from joints Parameter
Cement-lime mortar
Mortar samples from standard beams
Cement 2 mortar
Cement 1 mortar
Cementlime mortar
Cement 2 mortar
Cement 1 mortar
C
B
C
B
C
B
19.39
19.66
18.22
17.43
17.16
18.95
21.43
21.50
20.60
2.60
2.62
2.48
2.53
2.49
2.57
2.61
2.50
2.41
Volume density, [g/cm3]
2.09
2.10
2.03
2.09
2.07
2,08
2.05
1.96
1.91
Total pore area, [m2/g]
3.862
4.494
7.034
6.550
3.370
3,090
5.537
3.129
5.618
Pore diameter median (volume), [μm]
0.623
0.573
1.031
0.712
2.171
4,354
0.320
0.289
0.305
Pore diameter median (surface) [μm]
0.016
0.015
0.006
0.008
0.017
0,023
0.018
0.140
0.021
Porosity [%] Density (of skeleton), [g/cm3]
Marks of sample extraction place: C=central joint part, B=side joint part
0,14
Cumulative intrusion [mL/g]
0,12 0,1 0,08
Cement-lime mortar Cement 2 mortar Cement 1 mortar
0,06 0,04 0,02 0 1000000
100000
10000
1000 Diameter [nm]
100
10
1
Fig. 2. Porosity characteristics of tested mortars formed into beams in function of pore effective diameters.
In samples of tested mortars most of open pores are sized from 10-8 to 10-4 m. In case of cement 1 mortar pores responsible for capillary flow amount to 0.0383ml/g which equals 5.7 percentage points constituting 38% of general porosity (Fig. 2). For the other mortars pore volume responsible for capillary flow is similar and equals 0.026 ml/g, constituting about 4.9 percentage points. Figure 3 shows results of microstructure test of mortars formed in associated samples joints. Mortars cured in joints of associated joints indicate significant differences in microstructure parameters in relation to standard samples. Independent on mortar type, lower porosity values were noticed and higher pore diameter medians. In case of cement mortars there were also differences within the joints - samples taken from central and side parts differ
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both as to porosity values as well as to pore diameter medians. However, in case of cement-lime mortar the differences are small (Table 2). It is the effect of mortar workability and lime share. The analyze of curves obtained leads to a statement that independently of a mortar type, in the zone formed by contact with wall element there is higher porosity resulting from forming additional pores in the diameter range of 20000 nm (Fig. 3). a)
Cement 1 mortar
Cumulative intrusion, [mL/g]
0,14 0,12 0,1 0,08 0,06 0,04 0,02 0 1000000
b)
B C
100000
10000
1000 100 Diameter, [nm]
10
1
Cement-lime mortar
Cumulative intrusion, [mL/g]
0,14 0,12 0,1 0,08 B C
0,06 0,04 0,02 0 1000000
100000
10000
1000
100
10
1
Diameter, [nm] Cement 2 mortar 0,14 0,12 Cumulative intrusion, [mL/g]
c)
0,1 0,08 B C
0,06 0,04 0,02 0 1000000
100000
10000
1000
100
10
1
Diameter, [nm] Fig. 3. Porosity characteristics of tested mortars formed in joint of associated samples in function of pore effective diameter. Marking of sample place extraction according to Fig. 2: C=central joint part, B=side joint parts
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With detailed results of mortar porosity in the joint zones we can evaluate microstructure homogeneity by defining the difference between integral curve differential according to pore effective diameter or porosity in function of effective pore diameters, Jdif :
J dif = IVC − IVB ,
(2)
where: IVc - mercury intrusion for a particular diameter in a mortar sample taken from the central joint part, marked as C according to Fig. 2, IVB - mercury intrusion for a particular diameter in mortar sample taken from side joint parts, marked as B according to Fig. 2. It was assumed that mortar in the joint can be treated as homogenous if by comparison of integral curve differential distribution according to effective pore diameter the differences observed were less than 10% of maximum intrusion. The comparative analyses led by the author indicate that the resulting range of differences is: − 0,005mL / g ≤ J róĪ . ≤ 0,005mL / g
(3)
Within the range of diameters responsible for capillary flow (300 ÷ 3000 nm) only cement-lime mortar fulfilled the requirement formulated (Fig. 4). Cement 1 mortar1 Cementowa
Cement - lime mortar cementowo-wapienna
Cement 2 mortar cementowa 2
Pore volume difference, [mL/g]
0,01 0,0075 0,005 0,0025 3E-17 -0,0025 -0,005 -0,0075 -0,01 1000000
100000
10000
1000
100
10
1
Diameter, [nm] Fig. 4. Pore volume differences for mortars formed in joint for differential distributions.
The analysis of pore volume differences for integral distributions let define pore sized which as additional are formed in mortar in a joint part adjacent to wall element surface, marked as B in Fig. 2. Independently of mortar type in this zone there are additional pores created responsible for capillary flow. In cement mortars (Cement 1 and Cement 2) in this zone there are macropores formed.
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4. Conclusions The article presents the test results of three mortar types researched from the viewpoint of their roles in shaping the face wall integrity. Microstructure of mortar extracted from standard beams and associated samples were compared. It was found that addition of plasticizer to cement mortar causes significant increase of porosity while maintains the dominant diameter with its additional increase of share in general porosity. In cement mortar occurred high share of porosity responsible for capillary flow. Replacing the plasticizer with lime generates mortar structure with low share of pores responsible for capillary flow. For cement-lime mortar, the microstructure in the central and outer parts of joint is similar. Mortar with plasticizer indicates significantly lower volume density in the outer joint layer. As a result joint surface is created which decides about low joint quality. Based on the results obtained, it must be stated that integrity of face walls is ensured first of all with masonry mortar. It is a feature shaped as a result of a connection between a definite wall element and definite masonry mortar. Properly selected mortar should ensure tight connection with a wall element. Such connection is possible only when mortar will not change its features due to a correction of wall element placement: microstructure and bedding adhesion. Acknowledgements The work was done using apparatuses within the frame of „Realization of 2nd Stage of Regional Centre of Innovation” project, co-financed from means of the European Fund for Regional Development within the frame of Regional Operational Program of the Kujawsko – Pomorskie Voievodship for years 2007 – 2013. References [1] A. Moropoulou et al., Investigation of the technology of historic mortars Journal of Cultural Heritage. 1(1) (2000) 45–58. [2] M. Shigeishi, S. Colombo, K. J. Broughton, H. Rutledge, A. J. Batchelor, M. C. Forde, Acoustic emission to assess and monitor the integrity of bridges. 15(1) (2001) 35-49. [3] M. Arandigoyen, J.I. Alvarez: Pore structure and mechanical properties of cement–lime mortars Cement and Concrete Research. 37(5) (2007) 767–775. [4] J Lanas, José I Alvarez-Galindo, Masonry repair lime-based mortars: factors affecting the mechanical behavior, Cement and Concrete Research. 33(11) (2003) 1867–1876. [5] A.W Hendry Emeritus, Masonry walls: materials and construction, Construction and Building Materials. 15(8) (2001) 323–330. [6] A M Neville, Properties of Concrete, 3rd Edition, ELBS and Longman, Singapore, 1989. [7] A. Kamouna, A. Jelidi M. Chaabouni, Evaluation of the performance of sulfonated esparto grass lignin as a plasticizer–water reducer for cement, Cement and Concrete Research. 33(7) (2003) 995–1003. [8] A. A. Jeknavorian, E. Koehler, Use of Chemical Admixtures to Modify the Rheological Behavior of Cementitious Systems Containing Manufactured Aggregates, NRMCA Concrete Sustainability Conference proceedings, 2010. [9] Eurocode 6: Design of masonry structures - Part 2: Design considerations, selection of materials and execution of masonry. [10] J. Kubica, S. Gąsiorowski, Mortar Selectin in design practice – description of the problems, solutions and requirements. Architecture Civil Engineering Environment. 1 (2010) 53-61.
