# A Simple Benchmark to Evaluate the Influence Parameters of the Microstructure of the Masonry Wall on Capillary Water Migration Dynamic

Authors: Martial Nde Ngnihamye; Fabien Kenmogne; André Abanda; Michel Mbessa; Jean-De-La-Croix Gnappoun; Didier Fokwa
Journal: Advances in Civil Engineering
 (2022)

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## Abstract

The effects of masonry wall parameters on the water’s migration are deeply explored via the experimental laboratory simulation method. At this end, an experimental device consisting of a water tank in which a masonry block wall has a contact of around one centimeter with the water at its base is designed. The variation of the compactness of masonry blocks is obtained by compacting the concrete blocks with a hydraulic block press. The investigations consist of the monitoring of moisture front and moisture rate as a function of porosity, obtained by varying the compactness of the masonry wall, and the granular class of sand constituting the masonry. The determination of the granular sand classes was made from the NF P 18-101 standard. Three granular classes of sand were obtained using sand from the Logbadjeck quarry: 0/0.315 mm, 0.63/1.25 mm, and 2.5/5 mm. The obtained results show that the device is a good tool for the experimental analysis of the behavior of different masonry walls under water migration, which are in agreement with existing models in the literature.


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## Body

## 1. Introduction

Masonry is a construction system that has been widely used since the beginning of civilization and is still used throughout the world [1]. Building materials and those cementatious are the most used for the construction of structures. These materials are usually consisting of aggregates, cement, and water. Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together, and during the hydration process, the consistency of the material gradually changes from fluid to firm and then reaches the hardening of concrete.During the hydration process, several microstructural phenomena appear, leading to the creation of two forms of porosities. The ITZ around the aggregates, where the presence of aggregates belongs to a determined granular class, disturbs the normal evolution of the hydrates, leading to an increase in the porosity in this zone. The compaction by vibration or other means, of the cementatious materials during their implementation, modifies the microporous structure of the material but does not make it impermeable to the migration of moisture.It had been proved that the cementatious materials used in construction are essentially porous [2–5]. This is why they are subjected to almost permanent exchanges with their external environment, thus posing the durability problem of structures [6–9]. In fact, apart from the deterioration of the living comfort and health of the occupants, the migration of moisture in the microstructure of these materials, sometimes accompanied by the transport of aggressive agents, endangers the durability of the structure. Moreover, the increase in the moisture content can negatively impact the building’s heating process, leading to an increase in the power consumed during heating [10]. For these obvious reasons, it seems necessary to have a deepened knowledge of the hygrometric behavior of cementatious materials. Most works on this subject aim to highlight the extreme complexity of the dynamics of moisture migration in these cementatious materials, which present a highly microporous and very complex multiphase structure. This induces particular characteristics such as capillary absorption and hygroscopicity. This is why some authors conducted channeled reflections, focused on the role of the material’s microstructure in the dynamics of humidity migration [11, 12], and experimental tools have been developed [13–15], as well as mathematical models [16, 17].The aim of this work is to investigate experimentally the dynamics of moisture migration in masonry walls. To this end, a metrology will be developed which will allow the describing of the dynamic of moisture migration in an instrumented wall. Then, after having characterized the microstructure of the concrete blocks (porosity of ordinary and compacted concrete blocks, porosity in relation to the granular class of sand used for the manufacture of concrete blocks), the influence of the compactness will be first analyzed, following at the end by the analysis of the influence of a granular class of sand used for the manufacture of concrete blocks.


## 2. Materials

### 2.1. Origin of Raw Materials

The cement used to make the breeze blocks comes from the manufacturer Dangoté, whose production plant is located in the Douala IV subdivision. It is a compound Portland cement (CEM II 32.5), manufactured according to the NF EN197−1 standard, sold in 50 kg bags, and with a strength class of 32.5N/mm2. The mixing water necessary for the hydration of the cement comes from the Cameroon water utility corporation. Two types of sand are used independently, the Logbajeck quarry sand (LQS) (see Figure 1(a)) and the Moungo quarry sand (see Figure 1(b)). The LQS is used to highlight the influence of the granular classes. This sand is mainly composed of metamorphic rocks (gneiss) made up of quartz, mica, and feldspar, extracted from the Logbajeck quarry located about 50km from Douala. The MQS is used to highlight the influence of the compactness of the breeze blocks. This sand comes from a deposit whose parent rock is magmatic, of volcanic type (high concentration of quartz). This sand is extracted from the Moungo river bed by dredging with pumps, or in an artisanal manner using shovels and dugout canoes.Figure 1
Texture and visual appearance of sand samples (a) LQS and (b) MQS.
(a)(b)


### 2.2. Characterization of Raw Materials

The granulometric analysis of sand samples according to the NF EN 933-1 standard is carried out using an oven, a0.01g precision balance, and standardized sieves (Figures 2(a)–2(c)). The determination of the granular classes of sand is then carried out from the NF P 18−101 standard. These granular classes will be used to simulate in the laboratory their influence on the dynamics of moisture migration in the masonry wall.Figure 2
(a) Standardized sieves, (b) 0.01 g precision balance, (c) Oven.
(a)(b)(c)For the calculation of exact masses of sand necessary for the manufacture of the breeze blocks, the determination of the apparent densities of sands was carried out according to the prescriptions of the NF P 18-554 standard. Thus, after weighing the respective masses of the empty containerM1 and the container filled with the sand sample M2, and after measuring the volume V of the container, the apparent densities of the samples are determined by the following equation:(1)ρ=M2−M1V.


### 2.3. Composite Formulation and Manufacturing

The proportions of the mortar components taken into account in this experiment are those recommended by the manufacturer of the binder used (Dangoté Cement CPJ 32.5). TheW/C ratio is kept constant and equal to 0.5 for all manufactured mortars. The sand dosages, cement, and water per 110 liters of mortar are given in Table 1. After mixing the different components, 15×20×40cm3 and 20×20×40cm3 breeze blocks are produced manually (ordinary breeze blocks) and with the help of a breeze block press (vibrated breeze blocks) (Figure 3(a)). The block press used allows a pressure of about 5kg/mm3 to be applied. The breeze blocks are then cured for 72 hours, according to the requirements of the NF EN 13670 standard, to ensure complete hydration of the cement. The cure is followed by a drying period in ambient air, approximately 29oC for 168 hours.Table 1
Dosage of sand, cement and water necessary to have 110 liters of mortar.
ConstituentsUnitsDosagesCementKilogram (kg)50SandLiter (l)110WaterLiter (l)25Figure 3
(a) 20x20x40 cm breeze blocks and (b) cubic mortar blocks.
(a)(b)


### 2.4. Characterization of Composites

Cubic mortar blocks of dimensions4×4×4cm3 were made for the determination of the porosity of each simulated wall type (Figure 3(b)). A device for measuring the percolating porosity n of the blocs has been manufactured following the principle diagram of Figure 4 [6, 18–20]. The porosity is then determined by using the following equation:(2)n=M−MdVs×100,where M is the mass of the wet specimen after an imbibition time t, Md is the mass of the dry specimen, and VS is the volume of the specimen.Figure 4
Principle diagram for measuring percolating porosity.


## 2.1. Origin of Raw Materials

The cement used to make the breeze blocks comes from the manufacturer Dangoté, whose production plant is located in the Douala IV subdivision. It is a compound Portland cement (CEM II 32.5), manufactured according to the NF EN197−1 standard, sold in 50 kg bags, and with a strength class of 32.5N/mm2. The mixing water necessary for the hydration of the cement comes from the Cameroon water utility corporation. Two types of sand are used independently, the Logbajeck quarry sand (LQS) (see Figure 1(a)) and the Moungo quarry sand (see Figure 1(b)). The LQS is used to highlight the influence of the granular classes. This sand is mainly composed of metamorphic rocks (gneiss) made up of quartz, mica, and feldspar, extracted from the Logbajeck quarry located about 50km from Douala. The MQS is used to highlight the influence of the compactness of the breeze blocks. This sand comes from a deposit whose parent rock is magmatic, of volcanic type (high concentration of quartz). This sand is extracted from the Moungo river bed by dredging with pumps, or in an artisanal manner using shovels and dugout canoes.Figure 1
Texture and visual appearance of sand samples (a) LQS and (b) MQS.
(a)(b)


## 2.2. Characterization of Raw Materials

The granulometric analysis of sand samples according to the NF EN 933-1 standard is carried out using an oven, a0.01g precision balance, and standardized sieves (Figures 2(a)–2(c)). The determination of the granular classes of sand is then carried out from the NF P 18−101 standard. These granular classes will be used to simulate in the laboratory their influence on the dynamics of moisture migration in the masonry wall.Figure 2
(a) Standardized sieves, (b) 0.01 g precision balance, (c) Oven.
(a)(b)(c)For the calculation of exact masses of sand necessary for the manufacture of the breeze blocks, the determination of the apparent densities of sands was carried out according to the prescriptions of the NF P 18-554 standard. Thus, after weighing the respective masses of the empty containerM1 and the container filled with the sand sample M2, and after measuring the volume V of the container, the apparent densities of the samples are determined by the following equation:(1)ρ=M2−M1V.


## 2.3. Composite Formulation and Manufacturing

The proportions of the mortar components taken into account in this experiment are those recommended by the manufacturer of the binder used (Dangoté Cement CPJ 32.5). TheW/C ratio is kept constant and equal to 0.5 for all manufactured mortars. The sand dosages, cement, and water per 110 liters of mortar are given in Table 1. After mixing the different components, 15×20×40cm3 and 20×20×40cm3 breeze blocks are produced manually (ordinary breeze blocks) and with the help of a breeze block press (vibrated breeze blocks) (Figure 3(a)). The block press used allows a pressure of about 5kg/mm3 to be applied. The breeze blocks are then cured for 72 hours, according to the requirements of the NF EN 13670 standard, to ensure complete hydration of the cement. The cure is followed by a drying period in ambient air, approximately 29oC for 168 hours.Table 1
Dosage of sand, cement and water necessary to have 110 liters of mortar.
ConstituentsUnitsDosagesCementKilogram (kg)50SandLiter (l)110WaterLiter (l)25Figure 3
(a) 20x20x40 cm breeze blocks and (b) cubic mortar blocks.
(a)(b)


## 2.4. Characterization of Composites

Cubic mortar blocks of dimensions4×4×4cm3 were made for the determination of the porosity of each simulated wall type (Figure 3(b)). A device for measuring the percolating porosity n of the blocs has been manufactured following the principle diagram of Figure 4 [6, 18–20]. The porosity is then determined by using the following equation:(2)n=M−MdVs×100,where M is the mass of the wet specimen after an imbibition time t, Md is the mass of the dry specimen, and VS is the volume of the specimen.Figure 4
Principle diagram for measuring percolating porosity.


## 3. Experimental Benchmark

The schematic diagram of the entire device is shown in Figure5, where the purpose is to monitor the moisture front (wetting and saturation front, moisture gradient) and to assess the kinetics of the moisture gradient. This device includes a water storage tank (1) that ensures the water supply source, a supply line (2) that leads water to the water container, a discharge line (3), connected to a pump, that ensures the evacuation of excess water, a masonry wall (4), a computer (5), for data processing and the plotting of curves, a moisture sensor (6), for measuring of moistures rates, a water container (7), as an imbibition tank, a steel mesh support (8), to support the wall while letting the water pass, a baseplate (9) and a water tank support (11) as a support for the water container, thus blocking its deformations, a wall stabilization support (10). Other materials consist of a graduated ruler for measuring the heights of the wetting and saturation fronts, a stopwatch for recording time and time intervals between measurements, and a camera to capture the moisture gradient mapping on the walls.Figure 5
Schematic diagram of the experimental simulation benchmark of capillary water migration in the walls. (a) Elevation view along the length of the wall, (b) Top view, (c) Elevation view along the thickness of the wall, in which: (1) Water storage tank, (2) Supply line, (3) Discharge line, (4) Masonry wall, (5) Computer, (6) Humidity sensor, (7) Water container, (8) Steel mesh support, (9) Baseplate, (10) Wall stabilization support, (11) Water tank support, (12) Longitudinal meshing, (13) Transversal meshing.
(a)(b)


## 4. Experimental Method

The method used is an experimental simulation in the laboratory, allowing us to multiply the wall models from variations of porosity. The phenomenon studied is assumed to be instantaneous, and the wall is assumed to be homogeneous. The moisture migration is vertical upwards, along theo,z axis. In the o,x,y plane, the moisture flow is uniform. The experiment is performed at temperature T≈29±5C and ambient humidity RH≈81±2% controlled.The device works as follows: masonry wall (4) of given lengths40∼82cm, thickness 15∼20cm, and height 64cm is carried out suitably, using cement mortar bricks, and joints of 2cm thickness. Once carried out, the wall is then left for two (02) weeks for complete drying. To punctually follow the moisture profile on both sides, the wall is meshed using a cordex respecting a spatial step of 5 cm along the length and 3 cm across the thickness (see elements (12) and (13) in Figure 5). Moisture front heights are then measured using a transparent ruler suitably graduated to the nearest millimeter. Height measurements are made at each mesh point along the length from y=0cm to y=40∼82cm with a step of 5cm and along the thickness from x=0cm to x=15 to 20cm with a space step of 3cm (see Figure 6). The measurements are taken at a variable time interval between 1 and 24 hours. The moisture rates are measured at a variable time interval between 1∼24 hours, using the humidity sensor (6).Figure 6
Schematic diagram of the principle of monitoring the capillary migration of the moisture front and rate in the walls; (a) On the thickness (o, x), (b) On the length (o, y). e thickness, L length, hn humidity front at a given time tn, mn humidity front at a given time tn.
(a)(b)To follow the moisture rate in the masonry wall, the points are materialized at a height of 3 cm from the base of the wall, where the moisture sensors will be fixed punctually in order to have a specific moisture rate value, and at regular intervals of times. The percentage values of the moisture rates are routed to the computer (5) via a data acquisition system (Figure5(a)). The results of the experiment can be expressed in the form of characteristic coefficients of the wetting kinetics kw and the kinetics of saturation ks, or in graphical form. The characteristic coefficient of saturation kinetic is the slope of the curve of saturation, given by Equation (1), and the characteristic coefficient of the wetting kinetic is the slope of the curve of wetting, given by Equation (2).(3)ks=msaturation−minitialtsaturation−tinitial,kw=mwetting−minitialtwetting−tinitial,where msaturation is the moisture rate at saturation measured at the corresponding time tsaturation, mwetting is the wetting moisture rate measured at the corresponding time twetting, and minitial is the initial moisture rate, before wetting measured at the corresponding initial time tinitial. The graphical results give the spatial and temporal evolution of the wetting font through the wall, the spatial and temporal evolution of the saturation front, and the spatial and temporal evolution of the moisture rate time tn,


## 5. Results and Discussion

### 5.1. Raw Material Characteristics

The results of the particle size analysis of the LQS and MQS as shown in Figure7 show that globally all the grain sizes are in the fraction between 0.16mm and 5mm. The weight distribution of these sizes is well balanced in the sand samples. Furthermore, Hazen’s uniformity coefficients lead to 4.09 and 3.50 for the MQS and LQS, respectively, meaning a varied or spread-out grain size. Furthermore, according to the analysis, the curvature coefficients of different sand samples are higher than 1, proving its good grading (presence of a large variety of grain sizes). Calculations of the fineness modulus of the samples give 3.15 for the MQS, indicating a low presence of fine elements in this sample. In contrast, a fineness modulus equal to 2.45 for the LQS indicates a high presence of fine elements in this sample.Figure 7
Graph of the particle size distribution of the sand samples.For the preparation of mortars based on sand divided into granular classes, the determination of the granular classes was based on the NF P18−101 standard. Thus, we have identified three granular classes, for the SCL sample as shown in Figure 7. The granular classes considered are 0.16/0.315mm, 0.63/1.25mm, and 2.5/5mm.The results of the apparent densities of the LQS and MQS are reported in Table2. The unfractionated MQS is denser than the fractionated LQS samples. The density of the LQS increases when the granular class contains smaller grain sizes.Table 2
Results of apparent densities of the sand samples.
SamplesGranular classes (mm)Densityg/cm3LQS0/0.3151.4790.63/1.251.4102.5/51.359MQS0/51.582


### 5.2. Porosity Rate of Breeze Blocks

Let’s call VBBW the vibrated breeze block wall, OBBW the ordinary breeze block wall, andW1 the wall whose breeze blocks are made of granular class 0.16/0.315mm, W2 the wall whose breeze blocks are made of granular class 0.63/1.25mm, and W3 the wall whose breeze blocks are made of granular class 2.5/5mm. The results of the percolating porosities of the specimens are shown in the histogram in Figure 8. The porosity rate decreases when the specimen is compacted. Indeed, the compaction of the breeze blocks leads to a drop in the porosity rate of around 13.04%. In addition, the extreme granular classes have higher porosity rates. Thus, the porosity rate increases by 10.48% from W2 to W3 and by 4.11% from W1 to W3.Figure 8
Porosity rate of mortar specimens.


## 5.1. Raw Material Characteristics

The results of the particle size analysis of the LQS and MQS as shown in Figure7 show that globally all the grain sizes are in the fraction between 0.16mm and 5mm. The weight distribution of these sizes is well balanced in the sand samples. Furthermore, Hazen’s uniformity coefficients lead to 4.09 and 3.50 for the MQS and LQS, respectively, meaning a varied or spread-out grain size. Furthermore, according to the analysis, the curvature coefficients of different sand samples are higher than 1, proving its good grading (presence of a large variety of grain sizes). Calculations of the fineness modulus of the samples give 3.15 for the MQS, indicating a low presence of fine elements in this sample. In contrast, a fineness modulus equal to 2.45 for the LQS indicates a high presence of fine elements in this sample.Figure 7
Graph of the particle size distribution of the sand samples.For the preparation of mortars based on sand divided into granular classes, the determination of the granular classes was based on the NF P18−101 standard. Thus, we have identified three granular classes, for the SCL sample as shown in Figure 7. The granular classes considered are 0.16/0.315mm, 0.63/1.25mm, and 2.5/5mm.The results of the apparent densities of the LQS and MQS are reported in Table2. The unfractionated MQS is denser than the fractionated LQS samples. The density of the LQS increases when the granular class contains smaller grain sizes.Table 2
Results of apparent densities of the sand samples.
SamplesGranular classes (mm)Densityg/cm3LQS0/0.3151.4790.63/1.251.4102.5/51.359MQS0/51.582


## 5.2. Porosity Rate of Breeze Blocks

Let’s call VBBW the vibrated breeze block wall, OBBW the ordinary breeze block wall, andW1 the wall whose breeze blocks are made of granular class 0.16/0.315mm, W2 the wall whose breeze blocks are made of granular class 0.63/1.25mm, and W3 the wall whose breeze blocks are made of granular class 2.5/5mm. The results of the percolating porosities of the specimens are shown in the histogram in Figure 8. The porosity rate decreases when the specimen is compacted. Indeed, the compaction of the breeze blocks leads to a drop in the porosity rate of around 13.04%. In addition, the extreme granular classes have higher porosity rates. Thus, the porosity rate increases by 10.48% from W2 to W3 and by 4.11% from W1 to W3.Figure 8
Porosity rate of mortar specimens.


## 6. Presentation of the Results of the Experiment

### 6.1. Influence of the Compactness of Breeze Blocks on the Dynamics of Moisture Migration

#### 6.1.1. Spatial Distribution of Moisture Rate

Figure9 shows the moisture rate according to the thickness of the masonry, after 48 hours of imbibition of VBBW (dashed lines) and OBBW (solid lines). The distribution of the moisture gradient through the thickness shows a significant phase shift in the absorption kinetics of the two walls. Indeed, the capillary saturation velocity is higher in the case of VBBW than in OBBW.Figure 9
Curves of spatial distribution of moisture rates in walls.


#### 6.1.2. Temporal Evolution of the Moisture Rate

Figure10 shows the temporal evolution of the moisture rate of VBBW and OBBW, imbibed continuously for over 40 days. The curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of water saturation of the material. However, the absorption kinetics leading to this saturation state is greater for VBBW than for OBBW. Indeed, during the first phases of imbibition, wetting of the capillary walls occurs (mono-molecular absorption), which requires less time to cover the small pore surface that characterizes the VBBW microstructure compared to the large pore surface that characterizes the OBBW microstructure.Figure 10
Curve of temporal evolution of moisture rates in walls.In addition, saturation is quickly reached for OBBW. Indeed, after 15 days, saturation is reached in this wall, against 28 days for the VBBW. Indeed, during the capillary absorption process leading to the saturation of the capillary channels, once the wetting of the capillary cavities has taken place, the migration of moisture leading to the establishment of a continuous water film is faster and more accentuated in the smaller capillary channels distributed in the solid phase of the VBBW.It should also be noted that despite the high porosity of OBBW, the saturation moisture rate of this wall is lower than that of VBBW. Indeed, the saturation moisture rate in OBBW is54%, compared to 67% in VBBW. This is due to a resistance to moisture migration, caused by the coarser capillaries distributed in the OBBW, thus slowing down the migration of moisture. As illustrated by the characteristic values in Table 3, the low porosity rate of VBBW, as well as the high proportion of occluded pores and noninterconnected open pores formed during the vibration of these blocks during the manufacturing process, can give the wall a resistant character to moisture migration. However, this will be in contrast to the high proportion of smaller pore sizes and therefore favourable to high capillary absorption of moisture.Table 3
Characteristic values of wall moisture.
Wall typesSaturation speedSaturation rateComparative valuesVBBWksV=7.375%/dayHRsatV=66.75%ksO/ksV=0.85OBBWksO=6.25%/dayHRsatO=54%HRsatO/HRsatV=0.764


#### 6.1.3. Spatial Evolution of the Moisture Front

The evolution of the moisture fronts (wetting and saturation) of the VBBW (solid lines) and the OBBW (dashed lines) is illustrated in (Figure11). Moisture profiles are plotted along length (Figure 11(a)) and along thickness (Figure 11(b)). A higher saturation front appears for VBBW, compared to OBBW where the front level remains lower. The migration flows of the wetting and saturation fronts presented in Figures 12(a) and 12(b) corroborate this result. The dephasing between the two walls is justified by the reduction in pore size caused by the vibration of the blocks during their manufacture. The first immediate consequence is the prolonged time it will take for the liquid to migrate from one level of the wall to another; the second consequence is the slowness saturation of the pore network, as presented by the result in Figure 9. The resistance to moisture migration in OBBW is explained by the presence of a large proportion of large pores, which do not participate significantly in the dynamics of capillary moisture migration.Figure 11
Evolution of the moisture fronts of the VBBW (solid lines) and the OBBW (dashed lines).
(a)(b)Figure 12
Moisture migration flow in VBBW and OBBW: (a) Wetting rate, (b) Saturation rate.
(a)(b)


### 6.2. Influence of Granular Classes of Mortar Sand

#### 6.2.1. Temporal Evolution of the Moisture Rate

Figure13 shows the temporal evolution of the moisture rate of these walls after continuous imbibition for more than 36 days. On analysis, the flow curves, independently of the granular class, are globally well represented, and qualitatively in agreement with the works shown in [11, 14].Figure 13
Temporal evolution of moisture rate.The starting of the imbibition process shows a gap according to the granular class; thus, the wall M3 starts its saturation 6 days after the walls M1 and M2. After starting up, the curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of pseudosaturation. However, the absorption kinetics leading to this pseudosaturation state varies from one granular class to another as indicated by the characteristic values in Table4. These observations show the influence of the grain sizes of the granular class on the dynamics of moisture migration in walls. Migration kinetics and moisture rate at saturation decrease as the grain sizes of the granular class increase, which is in agreement with results found in [21].Table 4
Characteristic values of moisture fluxes and rates at pseudo-saturation.
Granular classesmmM3M2M12.5/50.63/1.250/0.315Max flow before saturation1.80%/day2.60%/day3.65%/dayMoisture rate at saturation20.75%30.50%47.50%Furthermore, the addition of aggregates to the cementatious matrix considerably modifies its porous microstructure, in the sense of increasing its tortuosity. The presence of the sand aggregate in the cementatious matrix acts as a barrier to gel and capillary pores, and although the ITZ is a moisture migration path, its highly sinuous nature increases with grain size, thus providing a resistant character to moisture migration.The high moisture absorption rate ofM1 could be explained by the high content of fine particles in this fraction. Indeed, the large amount of fines in the mortar absorbs a larger part of the mixing water, with the consequence of limiting the hydration process of the cement, which should however contribute to the modification of the capillary porosity in the sense of reducing the sizes of the capillary pores, and making them discontinuous.


#### 6.2.2. Temporal Evolution of the Wetting Front

Figure14 shows the temporal evolution of the wetting fonts of walls M1,M2, and M3. The capillary rise curves show that surface wetting occurs on average within an interval of 2 days during which the kinetics of the process vary from one granular class to another. It is important to note that the wetting height reached at this time also varies from one granular class to another and independently of these classes, and the level value of the front remains constant for the next 9 days, before gradually disappearing leaving discontinuous moisture gradients on the walls. As summarized by the characteristic values in Table 5, the wetting kinetics are slower for walls with large particle size granular classes, so are the step moisture fronts. In other words, the use of large particles in the manufacture of breeze blocks makes the wall resistant to rising damp.Figure 14
Temporal evolution of the wetting front.Table 5
Characteristic values of wetting kinetics and maximum wetting front heights for the different walls.
Granular classesmmM3M2M12.5−50.63−1.250−0.315Migration flow of the wetting front3.38cm/day5.65cm/day8.62cm/dayMaximum height of the wetting front7.42cm11.73cm18.18cm


#### 6.2.3. Spatial and Temporal Evolution of the Wetting Front

The temporal-spatial evolution of the moisture fronts of the walls is shown in Figures15(a) and 15(b) for wall M1, Figures 15(c) and 15(d) for M2, and Figures 15(e) and 15(f) for wall M3. The dynamics of moisture migration are moreimportant in breeze block walls containing sand of lowgranular classes M1:0.16/0.315mm and M2:0.63/1.25mm). In contrast, the wall M3 with the largest granular class of sand 2.5/5mm has a higher resistance to moisture migration as shown in Figures 16(a) and 16(b).Figure 15
Comparison of the spatial temporal evolution of moisture fronts.
(a)(b)Figure 16
Spatial and temporal evolution of wall moisture front profiles: ((a)-(b)) M1, ((c)-(d)) M2 and ((e)-(f)) M3.
(a)(b)(c)(d)(e)(f)


## 6.1. Influence of the Compactness of Breeze Blocks on the Dynamics of Moisture Migration

### 6.1.1. Spatial Distribution of Moisture Rate

Figure9 shows the moisture rate according to the thickness of the masonry, after 48 hours of imbibition of VBBW (dashed lines) and OBBW (solid lines). The distribution of the moisture gradient through the thickness shows a significant phase shift in the absorption kinetics of the two walls. Indeed, the capillary saturation velocity is higher in the case of VBBW than in OBBW.Figure 9
Curves of spatial distribution of moisture rates in walls.


### 6.1.2. Temporal Evolution of the Moisture Rate

Figure10 shows the temporal evolution of the moisture rate of VBBW and OBBW, imbibed continuously for over 40 days. The curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of water saturation of the material. However, the absorption kinetics leading to this saturation state is greater for VBBW than for OBBW. Indeed, during the first phases of imbibition, wetting of the capillary walls occurs (mono-molecular absorption), which requires less time to cover the small pore surface that characterizes the VBBW microstructure compared to the large pore surface that characterizes the OBBW microstructure.Figure 10
Curve of temporal evolution of moisture rates in walls.In addition, saturation is quickly reached for OBBW. Indeed, after 15 days, saturation is reached in this wall, against 28 days for the VBBW. Indeed, during the capillary absorption process leading to the saturation of the capillary channels, once the wetting of the capillary cavities has taken place, the migration of moisture leading to the establishment of a continuous water film is faster and more accentuated in the smaller capillary channels distributed in the solid phase of the VBBW.It should also be noted that despite the high porosity of OBBW, the saturation moisture rate of this wall is lower than that of VBBW. Indeed, the saturation moisture rate in OBBW is54%, compared to 67% in VBBW. This is due to a resistance to moisture migration, caused by the coarser capillaries distributed in the OBBW, thus slowing down the migration of moisture. As illustrated by the characteristic values in Table 3, the low porosity rate of VBBW, as well as the high proportion of occluded pores and noninterconnected open pores formed during the vibration of these blocks during the manufacturing process, can give the wall a resistant character to moisture migration. However, this will be in contrast to the high proportion of smaller pore sizes and therefore favourable to high capillary absorption of moisture.Table 3
Characteristic values of wall moisture.
Wall typesSaturation speedSaturation rateComparative valuesVBBWksV=7.375%/dayHRsatV=66.75%ksO/ksV=0.85OBBWksO=6.25%/dayHRsatO=54%HRsatO/HRsatV=0.764


### 6.1.3. Spatial Evolution of the Moisture Front

The evolution of the moisture fronts (wetting and saturation) of the VBBW (solid lines) and the OBBW (dashed lines) is illustrated in (Figure11). Moisture profiles are plotted along length (Figure 11(a)) and along thickness (Figure 11(b)). A higher saturation front appears for VBBW, compared to OBBW where the front level remains lower. The migration flows of the wetting and saturation fronts presented in Figures 12(a) and 12(b) corroborate this result. The dephasing between the two walls is justified by the reduction in pore size caused by the vibration of the blocks during their manufacture. The first immediate consequence is the prolonged time it will take for the liquid to migrate from one level of the wall to another; the second consequence is the slowness saturation of the pore network, as presented by the result in Figure 9. The resistance to moisture migration in OBBW is explained by the presence of a large proportion of large pores, which do not participate significantly in the dynamics of capillary moisture migration.Figure 11
Evolution of the moisture fronts of the VBBW (solid lines) and the OBBW (dashed lines).
(a)(b)Figure 12
Moisture migration flow in VBBW and OBBW: (a) Wetting rate, (b) Saturation rate.
(a)(b)


## 6.1.1. Spatial Distribution of Moisture Rate

Figure9 shows the moisture rate according to the thickness of the masonry, after 48 hours of imbibition of VBBW (dashed lines) and OBBW (solid lines). The distribution of the moisture gradient through the thickness shows a significant phase shift in the absorption kinetics of the two walls. Indeed, the capillary saturation velocity is higher in the case of VBBW than in OBBW.Figure 9
Curves of spatial distribution of moisture rates in walls.


## 6.1.2. Temporal Evolution of the Moisture Rate

Figure10 shows the temporal evolution of the moisture rate of VBBW and OBBW, imbibed continuously for over 40 days. The curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of water saturation of the material. However, the absorption kinetics leading to this saturation state is greater for VBBW than for OBBW. Indeed, during the first phases of imbibition, wetting of the capillary walls occurs (mono-molecular absorption), which requires less time to cover the small pore surface that characterizes the VBBW microstructure compared to the large pore surface that characterizes the OBBW microstructure.Figure 10
Curve of temporal evolution of moisture rates in walls.In addition, saturation is quickly reached for OBBW. Indeed, after 15 days, saturation is reached in this wall, against 28 days for the VBBW. Indeed, during the capillary absorption process leading to the saturation of the capillary channels, once the wetting of the capillary cavities has taken place, the migration of moisture leading to the establishment of a continuous water film is faster and more accentuated in the smaller capillary channels distributed in the solid phase of the VBBW.It should also be noted that despite the high porosity of OBBW, the saturation moisture rate of this wall is lower than that of VBBW. Indeed, the saturation moisture rate in OBBW is54%, compared to 67% in VBBW. This is due to a resistance to moisture migration, caused by the coarser capillaries distributed in the OBBW, thus slowing down the migration of moisture. As illustrated by the characteristic values in Table 3, the low porosity rate of VBBW, as well as the high proportion of occluded pores and noninterconnected open pores formed during the vibration of these blocks during the manufacturing process, can give the wall a resistant character to moisture migration. However, this will be in contrast to the high proportion of smaller pore sizes and therefore favourable to high capillary absorption of moisture.Table 3
Characteristic values of wall moisture.
Wall typesSaturation speedSaturation rateComparative valuesVBBWksV=7.375%/dayHRsatV=66.75%ksO/ksV=0.85OBBWksO=6.25%/dayHRsatO=54%HRsatO/HRsatV=0.764


## 6.1.3. Spatial Evolution of the Moisture Front

The evolution of the moisture fronts (wetting and saturation) of the VBBW (solid lines) and the OBBW (dashed lines) is illustrated in (Figure11). Moisture profiles are plotted along length (Figure 11(a)) and along thickness (Figure 11(b)). A higher saturation front appears for VBBW, compared to OBBW where the front level remains lower. The migration flows of the wetting and saturation fronts presented in Figures 12(a) and 12(b) corroborate this result. The dephasing between the two walls is justified by the reduction in pore size caused by the vibration of the blocks during their manufacture. The first immediate consequence is the prolonged time it will take for the liquid to migrate from one level of the wall to another; the second consequence is the slowness saturation of the pore network, as presented by the result in Figure 9. The resistance to moisture migration in OBBW is explained by the presence of a large proportion of large pores, which do not participate significantly in the dynamics of capillary moisture migration.Figure 11
Evolution of the moisture fronts of the VBBW (solid lines) and the OBBW (dashed lines).
(a)(b)Figure 12
Moisture migration flow in VBBW and OBBW: (a) Wetting rate, (b) Saturation rate.
(a)(b)


## 6.2. Influence of Granular Classes of Mortar Sand

### 6.2.1. Temporal Evolution of the Moisture Rate

Figure13 shows the temporal evolution of the moisture rate of these walls after continuous imbibition for more than 36 days. On analysis, the flow curves, independently of the granular class, are globally well represented, and qualitatively in agreement with the works shown in [11, 14].Figure 13
Temporal evolution of moisture rate.The starting of the imbibition process shows a gap according to the granular class; thus, the wall M3 starts its saturation 6 days after the walls M1 and M2. After starting up, the curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of pseudosaturation. However, the absorption kinetics leading to this pseudosaturation state varies from one granular class to another as indicated by the characteristic values in Table4. These observations show the influence of the grain sizes of the granular class on the dynamics of moisture migration in walls. Migration kinetics and moisture rate at saturation decrease as the grain sizes of the granular class increase, which is in agreement with results found in [21].Table 4
Characteristic values of moisture fluxes and rates at pseudo-saturation.
Granular classesmmM3M2M12.5/50.63/1.250/0.315Max flow before saturation1.80%/day2.60%/day3.65%/dayMoisture rate at saturation20.75%30.50%47.50%Furthermore, the addition of aggregates to the cementatious matrix considerably modifies its porous microstructure, in the sense of increasing its tortuosity. The presence of the sand aggregate in the cementatious matrix acts as a barrier to gel and capillary pores, and although the ITZ is a moisture migration path, its highly sinuous nature increases with grain size, thus providing a resistant character to moisture migration.The high moisture absorption rate ofM1 could be explained by the high content of fine particles in this fraction. Indeed, the large amount of fines in the mortar absorbs a larger part of the mixing water, with the consequence of limiting the hydration process of the cement, which should however contribute to the modification of the capillary porosity in the sense of reducing the sizes of the capillary pores, and making them discontinuous.


### 6.2.2. Temporal Evolution of the Wetting Front

Figure14 shows the temporal evolution of the wetting fonts of walls M1,M2, and M3. The capillary rise curves show that surface wetting occurs on average within an interval of 2 days during which the kinetics of the process vary from one granular class to another. It is important to note that the wetting height reached at this time also varies from one granular class to another and independently of these classes, and the level value of the front remains constant for the next 9 days, before gradually disappearing leaving discontinuous moisture gradients on the walls. As summarized by the characteristic values in Table 5, the wetting kinetics are slower for walls with large particle size granular classes, so are the step moisture fronts. In other words, the use of large particles in the manufacture of breeze blocks makes the wall resistant to rising damp.Figure 14
Temporal evolution of the wetting front.Table 5
Characteristic values of wetting kinetics and maximum wetting front heights for the different walls.
Granular classesmmM3M2M12.5−50.63−1.250−0.315Migration flow of the wetting front3.38cm/day5.65cm/day8.62cm/dayMaximum height of the wetting front7.42cm11.73cm18.18cm


### 6.2.3. Spatial and Temporal Evolution of the Wetting Front

The temporal-spatial evolution of the moisture fronts of the walls is shown in Figures15(a) and 15(b) for wall M1, Figures 15(c) and 15(d) for M2, and Figures 15(e) and 15(f) for wall M3. The dynamics of moisture migration are moreimportant in breeze block walls containing sand of lowgranular classes M1:0.16/0.315mm and M2:0.63/1.25mm). In contrast, the wall M3 with the largest granular class of sand 2.5/5mm has a higher resistance to moisture migration as shown in Figures 16(a) and 16(b).Figure 15
Comparison of the spatial temporal evolution of moisture fronts.
(a)(b)Figure 16
Spatial and temporal evolution of wall moisture front profiles: ((a)-(b)) M1, ((c)-(d)) M2 and ((e)-(f)) M3.
(a)(b)(c)(d)(e)(f)


## 6.2.1. Temporal Evolution of the Moisture Rate

Figure13 shows the temporal evolution of the moisture rate of these walls after continuous imbibition for more than 36 days. On analysis, the flow curves, independently of the granular class, are globally well represented, and qualitatively in agreement with the works shown in [11, 14].Figure 13
Temporal evolution of moisture rate.The starting of the imbibition process shows a gap according to the granular class; thus, the wall M3 starts its saturation 6 days after the walls M1 and M2. After starting up, the curves have the same increasing paces and then evolve in an approximately horizontal step, characterizing a state of pseudosaturation. However, the absorption kinetics leading to this pseudosaturation state varies from one granular class to another as indicated by the characteristic values in Table4. These observations show the influence of the grain sizes of the granular class on the dynamics of moisture migration in walls. Migration kinetics and moisture rate at saturation decrease as the grain sizes of the granular class increase, which is in agreement with results found in [21].Table 4
Characteristic values of moisture fluxes and rates at pseudo-saturation.
Granular classesmmM3M2M12.5/50.63/1.250/0.315Max flow before saturation1.80%/day2.60%/day3.65%/dayMoisture rate at saturation20.75%30.50%47.50%Furthermore, the addition of aggregates to the cementatious matrix considerably modifies its porous microstructure, in the sense of increasing its tortuosity. The presence of the sand aggregate in the cementatious matrix acts as a barrier to gel and capillary pores, and although the ITZ is a moisture migration path, its highly sinuous nature increases with grain size, thus providing a resistant character to moisture migration.The high moisture absorption rate ofM1 could be explained by the high content of fine particles in this fraction. Indeed, the large amount of fines in the mortar absorbs a larger part of the mixing water, with the consequence of limiting the hydration process of the cement, which should however contribute to the modification of the capillary porosity in the sense of reducing the sizes of the capillary pores, and making them discontinuous.


## 6.2.2. Temporal Evolution of the Wetting Front

Figure14 shows the temporal evolution of the wetting fonts of walls M1,M2, and M3. The capillary rise curves show that surface wetting occurs on average within an interval of 2 days during which the kinetics of the process vary from one granular class to another. It is important to note that the wetting height reached at this time also varies from one granular class to another and independently of these classes, and the level value of the front remains constant for the next 9 days, before gradually disappearing leaving discontinuous moisture gradients on the walls. As summarized by the characteristic values in Table 5, the wetting kinetics are slower for walls with large particle size granular classes, so are the step moisture fronts. In other words, the use of large particles in the manufacture of breeze blocks makes the wall resistant to rising damp.Figure 14
Temporal evolution of the wetting front.Table 5
Characteristic values of wetting kinetics and maximum wetting front heights for the different walls.
Granular classesmmM3M2M12.5−50.63−1.250−0.315Migration flow of the wetting front3.38cm/day5.65cm/day8.62cm/dayMaximum height of the wetting front7.42cm11.73cm18.18cm


## 6.2.3. Spatial and Temporal Evolution of the Wetting Front

The temporal-spatial evolution of the moisture fronts of the walls is shown in Figures15(a) and 15(b) for wall M1, Figures 15(c) and 15(d) for M2, and Figures 15(e) and 15(f) for wall M3. The dynamics of moisture migration are moreimportant in breeze block walls containing sand of lowgranular classes M1:0.16/0.315mm and M2:0.63/1.25mm). In contrast, the wall M3 with the largest granular class of sand 2.5/5mm has a higher resistance to moisture migration as shown in Figures 16(a) and 16(b).Figure 15
Comparison of the spatial temporal evolution of moisture fronts.
(a)(b)Figure 16
Spatial and temporal evolution of wall moisture front profiles: ((a)-(b)) M1, ((c)-(d)) M2 and ((e)-(f)) M3.
(a)(b)(c)(d)(e)(f)


## 7. Conclusion

The realization of a device used to study the dynamics of moisture migration in masonry wall was the subject developed throughout this study and contributed to highlight the effects of compactness and granular class constituting the breeze block. Then, it appears that the normalized vibration of concrete blocks leads to a drop in the porosity rate, the disconnection of interconnected open pores, and the establishment of occluded pores. These modifications grant the wall resistance to moisture migration, but the impact of which is reduced by the pore sizes will be considerably reduced during the vibration process and therefore leads to increase in the migration dynamic. Large aggregates allow to obtain porous concrete blocks, with large pore sizes, resistant to capillary rising damp. This simple device is also a way to assess the rate of influence ofW/C ratio, cement dosage, and cement hydration degree of breeze blocks, on moisture dynamic in the wall; this would be possible with a larger database. We also want to see this device improved through the addition of a quantified pressure variation accessory, with automation of some controls making the device more convenient and reliable.



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*Source: 9292794-2022-10-03.xml*