423

DETERMINATION OF MOISTURE CONTENT IN MASONRY MATERIALS: CALIBRATION OF SOME

DIRECT METHODS

BINDA , l., DIS, Politecnico of Milan Milan, Italy

SQUARCINA, T ICITE-CNR, S.Giuliano M. (Ml). Italy

VAN HEES, R. TNO, Delft, Netherland

ABSTRACT

The presence of moisture in masonry walls is always a direct or indirect source of damage: the aesthetics of the building, the performance of the materials and the in-door hygrothermic conditions can heavily change when the moisture content exceeds the normal hygroscopic value. The determination of the moisture profile of the wall is essential for several purposes, particularly for a correct diagnosis of current pathology and for the evaluation of the effectiveness of water-repellent treatments and measures against rising damp. Furthermore quantitative methods, if any, could provide the absolute values of moisture content necessary both to : (i) calibrate indirect non destructive methods, like the electrical or the radar ones, the infrared thermography or others, (ii) be used as input values for the mathematical models for moisture transport. A calibration is also necessary for direct methods such as the gravimetric one when very small quantities of the material are sampled; in fact different ways of sampling can significantly affect the accuracy of the measure. As a matter of fact sampling by chisel, core drilling or powder drilling, that is usually chosen according to the maximum allowed level of destruction, can influence the amount of water evaporation depending on the heating of the sampling tools. Moreover, even the precision of a direct method may vary when it is applied to materials with different porous structure, hardness and saturation level. The calibration of two techniques for measuring the moisture content is presented : the powder drilling and the calcium carbide. The tests are carried out following some proposals for recommendation presented to the 127MS RILEM Committee by BRE, GB and TNO, Netherland. The materials tested were new and historic bricks, soft and hard stones. The tests were carried out in laboratory and on site on phisical models and real historic buildings. The possibility has been checked also to assess moisture and salt profiles.

INTRODUCTION

The determination of the moisture and salt content in a masonry wall is always useful for research purposes and in real cases every time the presence of water is supposed to be the cause of existing and future damages to the wall surface. Furthermore it is also useful especially when protective techniques like surface treatments or interventions to stop capillary rise of moisture have to be applied. Measurement techniques of different type and order have been so far proposed in these last years based on: i) the external surface moisture content, ii) sampling and weighing of the sample dried to constant mass, iii) on site use of internal probes, iv) non destructive evaluation techniques (NDT) like infrared thermography, near infrared reflectance spectroscopy, and even radar. Even if each one of these methods can be successfully applied to specific cases, for none of them the knowledge is so deep that it can be codified or standardised and the international research community is still puzzling on the

(*) DIS, Politecnico of Milan, Milan, Italy (**) ICITE-CNR, S.Giuliano M. (Ml), Italy (***) TNO, Delft, Netherland

424

solution of the problems. The reason for this difficulty is based on the influence each method has on the real water content of the masonry and especially on the influence of high inhomogeneity of the masonry on the moisture variation inside the wall. Methods based on the measurement of surface moisture content using simple probes give only a partial information on the wall and are subject to the continuous variation of the water content near the surface due to the evaporation conditions. Methods based on sampling and gravimetric detection of the moisture can be easily used to find the variation in moisture content inside the wall at different depth and give also information on the distribution gradient of water and salts, but the operation of sampling can change heavily the real moisture content due to the heating of the sample caused by the drill; furthermore these methods are destructive and the moisture control along the time is only possible in a nearby situation. The use of moisture probes inside the wall at different depth allows for a continuous monitoring of the situation even in the case when walls are protected from rain penetration and/or consolidated or when macro-porous renders or injections against the capillary rise are applied; the limits of these techniques are given by the presence of salts which can influence the measurements or may cause corrosion of the probes and by the still high costs of the equipments. NDTs can be successfully used, but they still do not give any quantitative results and may be they will become useful in a near future. Among the mentioned techniques for measurement of the moisture content, those based on powder drilling and bulk weighing are certainly the most applied in the case of historic buildings; these techniques even if slightly destructive are easy and cheap and can give a great deal of information for the diagnosis and the control of intervention efficiency. Nevertheless a number of doubts have been expressed by many researchers on the accuracy of the results given by the drilling methods even if several proposals have been done for codes and recommendation: the Italian Recommendations supported by the Ministry of Cultural Properties (NORMAL), the drafts of the RlLEM Technical Committee 127MS (masonry structures), the Netherlands standard, all contain the description of similar methods based on drilling of some powder from the masonry and calculating the water content by weighing the sample soon after drilling and after taking it dry at constant mass. The methods differ slightly one from the other, but the principle is the same and also the risks of error are similar. The difficulty of achieving reliable values are also due to the fact that they sare applied to masonry materials which can highly differ in porosity and strength one from the other. The first step toward the definition of the reliability of a test method is certainly the calibration of the method to the different application by comparison with a reference test which has been so far already proved reliable. The authors took the opportunity to calibrate the drilling test methods offered by a collaboration within two European contracts (EV5V-CT92-0108 and EV5V-CT94-0515) on the durability of masonry and of their surface treatments. The results of the drilling method on one type of brick and two type of stones, a soft calcareous stone and a sandstone were compared with the results of the gravimetric method applied to the entire brick or stone at different moisture content; calibration curves are proposed for the different materials establishing the percentage of variation from the reference test. Laboratory tests on materials and in situ tests on experimental full-scale models were carried on according to the method by British Research Establishment, which has also proposed a Recommendation draft to RILEM TC127MS. Besides some applications are given on site base on the long experience by TNO, according to NL Standard NEN 2778.

1. LABO RA TORY EXPERIMENTAL RESULTS

It is well-known that the moisture content of a porous material depends upon the external conditions and the porosity of the material itself, that is pore size distribution. In the case of

425

masonry, the water can be supplied by capillary rise, by rain penetration, by condensation of water vapour fed in the wall by different causes, etc. When water is trapped into the masonry, it can migrate and also solubilize eventual salts contained into the material itself or coming from the soil or from dry and wet depositions on the external surface of the masonry. Different environmental attacks can cause damage to the wall when the water or salt solutions are present; in these cases the knowledge of the water and salt content in the walls can help finding appropriate solutions to avoid damage. As it was previously mentioned the calculation of the percentage of water content in a masonry done on the basis of experimental data is not so easy due to the difficulty of applying reliable measurement procedure to the difficult case of masonry. Therefore each procedure has to be calibrated to the specific material and component of the wall.

1.1 Description of the method and of the calibration test The drilling method follows the standardised procedure proposed by BRE [1] and TNO [2], briefly described in the following. The bit is a 10 mm diameter (15 mm for TNO) and 200 mm long; the drill is hand held with a thrust sufficient to penetrate the whole depths of units (55 mm) in maximum 25+30 seconds. The drilled samples were collected by an aluminium chute in a crucible or in a sample tube; the bit was frequently removed from the hole to clear the powder and then cooled by immersion in methylated spirits after each drilling. A convenient sample weight is considered approximately 6 g (10 g for TNO). Both moisture content and hygroscopic moisture content at a defined percentage of R.H. can be determined on the same drilled samples in order to show the presence of some hygroscopic salts. The determination of sulphates content can also be obtained by chemical analysis on the same samples in order to correlate these values with hygroscopic moisture content. If both determination of moisture content and hygroscopic moisture content are required, at first a few grams of material were put on watch glasses, weighted and placed immediately in a dessicator in which a saturated sodium chloride solution provides a 75 % R.H. (or potassium nitrate for a 92+95% R.H.). When constant masses were reached, the same samples were dried in oven at 105 °C to determine the moisture content. Moisture content (M.C.) and hygroscopic moisture content (H.M.C.) were calculated as follows :

M.C.= ww -wd *100 wd

H.M.C.= W 1so;. -wd *100 wd

As it can be argued from the description of the method this is not easily applied to every material. Due to the heat developed during the drilling the material can loose a certain percentage of water content clearly depending on its opposition to penetration; the speed of the drill itself can obviously influence this loss of water and even the pressure exerted by the operator can produce large scattering of the results. Furthermore during the calibration of the methods also the saturation degree of materials has to be considered as a parameter influencing the loss of moisture. In order to check the reliability of the method and its limits of application, three different types of materials were tested in different state of moisture: a soft­mud brick of new production, used in Italy for restoration works, a sandstone of the type of Serena stone used in the central part of Italy and a calcareous stone called improperly "tuff" used in the southern part of Italy still nowadays for small constructions. The physical properties of the three materials are listed in Table 1.

426

Brick "Tuff'' Serena sandstone

Volume of open porosity (%) 41.78 33.76 3.01 J.mercu_ry_Qorosimeter methoq}_ Water absorption after 26 23.5 2.4 com_Qlete immersionl0/o C!!Y weight) Elapsed time to reach saturation (h) 24 8 192

Elapsed time for a complete drying 340 150 55 at 20°c and 50% R.H. J.~ Max. suction due to capillary rise(kg/m"'Z) 90 30 3

Bulk density (kg/m~) 1550 1582 2650

Table 1 - Physical properties of the three tested materials

1

2 .

3 .

4 .

5.

•

Fig. 1 - Scheme of the drillings

Reference units (1200x2500x55mm) were used to calculate the moisture content of the three materials at different conditions as follows: the units were prepared for the test by saturating them in water by total immersion and put into an oven for different drying times in order to reach different degrees of moisture content. Samples of powdered material were drilled from different units or from the same reference units on which the bulk moisture content was measured soon after it was taken from the oven. The drilling was carried on in fiv.e different points along the diagonal of the unit through the whole thickness of the material in order to have a comprehensive and representative sampling for the unit. The moisture content was measured from the drilled samples (Fig. 1). At least fifteen units were tested for each material. The moisture content of the units was plotted against the moisture content of the

drilled samples every time, according to the procedure presented in [ 1] .

1.2 Influence of drill speed Two drills with different speed were used according to [1], [2] to calibrate drilling method: drill A had a variable speed between 700 and 2000 rpm while drill B had 0-:-700 rpm. 56 units of soft mud brick were tested with drill A and 42 with drill B ; the number of sandstone units used was 46 (drill A) and 20 (drill B). In figs. 2a,b and 3,a,b the results are plotted for the bricks and the Serena sandstone. Concerning the brick, the calibration curves appear to be very similar one to the other; some comments can more precisely describe every step: • great scatter and high difference among the average values of drillings from bulk moisture

content was obtained with both drill speeds; • from 5 to 20 per cent bulk moisture content, comparable results are shown in both the

curves with quite constant difference from real moisture content ; • the moisture content of drillings exceeds the bulk moisture content at saturation (drill B)

probably due to the following effect: some water evaporated due to the drilling heating is counteracted by the ability of powdered sample to absorb water from the surrounding brick [l].

Concerning the Serena sandstone it could be observed that: • much more accurate results was obtained by lower speed drill on this hard material, even

when moisture content is close to saturation;

Brick Drill A

/ ~ 20 f-:::=::t===i=~-+-----;JL,e.__j_ _ _J ~ :g 15 r-------t---t-"'--71'---,:C.-+---l----< -0

c ~ 10r-------t--,l'-F----l--+---l----<

8 !!:> 5 r-------;:;t7t--t---t--t--+--1 :J iii ' (5 0 -----~-~--'------'-----'----' E 0 5 10 15 20 25 30

bulk moisture content (%dry weight)

427

~ 30 1r::::c::==r::;--r-r--i-71 ~

-0 25 ~ Ill

Brick Drill B

l 20 r---t--t--+----,i!-.--+-~

~ 15 r---t--t--:>f7'--11----+--l c ~ 10 r------t---;f--'or---+---i---l---~ 0 ()

~ 5 r-------7!'-?---t--+--I---+-~ en • /• '6 P. E 0 .__...._,_ _ _,__ _ _j____J _ __L_ _ _J

0 5 10 15 20 25 30

bulk moisture content (% dry weight)

Fig. 2a, b - Calibration curves for soft mud bricks according to different speeds of the drill

~ 2.5 r---.,--.-----,.--~-~,, ~

"O

~ 2.0 Ill Cl

Serena sandstone // Drill A

:§ 1.5 t---t--+--+-----'4----l ~ -0

0.5 1.0 1.5 2.0 2.5

bulk moisture content (%dry weight)

~ 2.5 ~

"O

~ 2.0 Ill Cl

:§ 1.5 ~ 0 c 1.0 Q)

c 0 ()

~ 0.5 :J iii '6 E 0.0

,

Serena sandstone / r- DrillB

~ ,/ v ~ ~

~

__:_

lL 0.0 0.5 1.0 1.5 2.0 2.5

bulk moisture content (% dry weight)

Fig. 3a. b - Calibration curves for Serena sandstone according to different speeds of the drill

• a little scatter is always shown, especially if we consider how low is the absolute moisture content (due to the low porosity of the material).

1.3 Influence of the reference unit Two different methods were subsequently followed assuming a reference unit in different ways in order to better calibrate the results: a) the bulk moisture content at different times of drying was determined on a reference unit different from the ones from which powdered samples were drilled. The results of the test are plotted in Figs. 4a, b for the brick and the "tufP' . The conditions of saturation and drying were the same for the reference unit and the tested units, being the oven temperature constant and the times of drying the same; nevertheless the results show a great scattering, particularly for the sandstone due to the high strength and low porosity of the material; b) the reference unit was the same unit from which the samples were drilled at different times of drying into the oven. After drying the unit was weighed and rapidly the samples were drilled and subsequently weighed. This method was applied only to the brick and the calcareous stone. Figs. Sa, b show the resulting plots where, of course, the data are much less scattered and the differences seem much lower than in the case of method a).

3 30 r;::::::=====::::;-r-----,~

ti Brick / / ~ 25 Reference method A rJ)

gi 20 1--------l----l--+------,!<;te----+-----1

·.:::: i:::J

0 15

c Q) 10 1--------l--~~+----+----+-----1 c 0 u Q) 5 ._______.,._ ___ -+-- +---+--+--------1

:; en 6 E 5 10 15 20 25 30

bulk moisture content(% d. w.)

428

Tuff / Reference method A

ci ~

Al

•

~ ·1W =

kt: • . · d .

,,,f' . . •

ti ::R 25 ~ Ol c 20

:g - 15 0

c Q)

10 c 0 u ~ 5 ::J en ·5 0 E o 5 10 15 20 25 30

bulk moisture content (% d. w.)

Fig. 4a, b - Calibration curves for soft mud brick and "tuff' according to reference method A

~ 30 / ti Brick • / : 25 Reference method B I / g> 20 ~--+---+--+---->f'ld'.__7---t----1 ·-== I J7 i:::J 15 ~--+---+--r~~~"-+--t----i ~ k;/·/ Q) 10 ~--+----.!'-c~~~-+----t--t-----1

§ ~v Q) 5 /

~ /-' en ,,r "(5 0 .._---'-----'---_.__--+--+-~ E o 5 10 15 20 25 30

bulk moisture content(% d. w.)

~ 30 r;:::=====::::;-r-1~ ti ~ 25 rJ)

Tuff Reference method B

gi 20 l---+----t--t-----;>f-7"--r---1

·.:::: i:::J 15 f---+--+----,fr---+----t---1 0 c Q) 10 1---+--u--i-----t---r---1 c 0 u ~ 5 f-----,l"~-+--r---+--;-------1 ::J (ii ·5 0 ~~-~-~~---E O 5 10 15 20 25 30

bulk moisture content(% d. w.)

Fig. 5a, b - Calibration curves for soft mud brick and "tuff' according to reference method B

2. COMPARISON WITH THE CALCIUM CARBIDE METHOD

The measurements of moisture content by calcium carbide method [3] were carried out on the same units used for the gravimetric determinations, drilling samples from five holes along the other diagonal of the unit (fig. 6) and mixing all the powders together. 20 g of this grit coming from each single unit was mixed with a known quantity of calcium carbide in a closed

• 7•

8.

9•

bottle, measuring the pressure increase due to the acetylene gas formed by the reaction of moisture with calcium-carbide. 83 units of soft mud bricks were tested according to reference method A (see above) and 21 with reference method B, while 12 units (ref. method A) and 15 units (ref. method B) were used concerning "tuff'' . The results are presented by plotting the moisture content determined by gravimetric method on drilled samples versus moisture content determined by calcium-carbide method (see figs . 7a,b and 8a,b). Calcium carbide method nearly always gives higher values of moisture content than the ones obtained with gravimetric method on powdered samples with reference method B, even higher than bulk moisture content. In the case of method A the curves obtained are Fig. 6 - Scheme of the

drillings not reliable due to the large scattering of the results.

3 30 ,------,-----,....--~---~ -0 ~ 25

Brick Reference method A

g 20 ----,----,---~-' u

iii ·5 15 r---t---t---.-.,p!.---+~r-l----l

E Q)

10 'O :.0 (ij u 5 E :J ·u 0 (ij u 0 5 10 15 20 25 30

gravimetric method moist. cont. (% d. w.)

429

3 30 r:==::r====:=T--r~

~ 25

i 20 0

u

iii 15 ·5

E Q) 'O 10 15 <o u 5 E :J ·u 0 (ij

0 u

Brick Reference method B

~ . 5 10 15 20 25 30

gravimetric method moist. cont. (% d. w.)

Fig. 7a,b - Calibration curve for calcium-carbide method versus gravimetric method on drilled samples for soft mud brick

i 30 r;==r::==::r:::::::::r:==::r------ir-71 -0 Tuff ~ 25 Reference method A

"' g> 20 t---+--+--+----'---+---;

~ 15 1---+--f-----,,ftl--,,.4-~--l 0 c Q) 10 >---+--<'--'----+----+- ----+--------' c 0 u ~ 5 >----"'-"'-......... ~+----+---1--------'

:J iii ·5 0 ~--+--~-+--~---!-~ E O 5 10 15 20 25 30

gravimetric method moist.cont. (% d. w.)

i' 30 r.======::::;,---,-,,, -0 Tuff ~ 25 Reference method B

"' g> 20 >----+---+--_.____."'----"--'----'

~ 15 0 1-----1--_._'--JL.--l---1---l

c $ 10 1------!-~__,jL--.l--_j_--l---l c 0 u ~ 5 1----..77!'----4--l---l-------l-~

~ I/ ·5 0 "----'----'--'-----'---'----' E o 5 10 15 20 25 30

gravimetric method moist. cont. (% d. w .)

Fig. 8a,b - Calibration curve for calcium-carbide method vs gravimetric method on drilled samples for tu.ff

3. IN-SITU APPLICATIONS

Determinations of moisture content and hygroscopic moisture content were carried on in a systematic way in-situ on outdoor physical full-scale models, and on real historic buildings.

3.1 Outdoor physical models Determination of moisture content on real walls of full-scale models was carried out by the drilling method calibrated in laboratory on the same materials used to build the models [ 4]. These brick walls are 25 cm thick and drillings were made in order to outline the different moisture contents existing at different depths in the wall as well as at different heights; as a matter of fact, the drilling method allows to draw horizontal and vertical moisture profiles [ 5]. 4 drilling series were carried on these walls, each one consisting of 5 drilling levels (20, 40, 60, 80, 100 cm from ground level), each one at three different depths inside the walls: 0-:-8 cm (internal part of the wall), 8-:- 16 cm (middle part of the wall), 16-:-24 cm (external part of the wall). Therefore 15 samples were cored for each drilling series. Sulphates contents were also determinated by chemical analysis only on eight of the samples. The weather conditions during the campaigns of drilling were in absolute absence of rain so that the presence of moisture content in the walls can be totally attributed to the action of the capillary rise allowed from the soil.

35

30

~25 0 --c: 2 20 c: 0 0

~ 15 ::::::J -(/)

-~ 10

5

--I--

I--

I--~

I"" ~ -I--

i... ....

I--

0 J. J_ J_ l J_ l J_ J_ J_

int. o 8 16

depth of drilling (cm)

430

Level

--1- 100cm

-+-- 80cm

------60cm

___...__ 40cm __.._ 20cm

24 ext.

Fig. 9 - Horizontal profiles of moisture content for drilling series l

The powder drilled out of the walls was closed into some glass bottles tightly covered and rapidly transported to the laboratory for the determination of moisture content. Figs. 9, 10, 11 show respectively the horizontal profiles at each drilling level, the vertical profiles at each depth of drilling and the vertical hygroscopic moisture content profiles for the drilling series I . Sulphates contents of some drilled samples determinated by chemical analysis in comparison with their hygroscopic moisture content are reported in tab 2. Horizontal and vertical profiles of moisture content show that values decrease with the height of the wall; furthermore higher values were quite always found in the central part of

the section of the wall at every height from the ground level. These results are precisely the ones to be expected in a wall subjected to the action of capillary rise. Hygroscopic moisture behaviour of material was determinated at 75 % R.H. and very low values were obtained except for the lower parts of the walls were probably some salts were absorbed by the soil. A correlation between hygroscopic moisture content and sulphates content cannot be done due to the found low values.

100 100

Depth of drilling

__.....__ 0-8cm

80 - 8-16 cm 80 ,-...

---- 16-24 cm ,-...

E E 0 0 - -Q) Qi > > 60 ~ 60 ~

Cl Cl c: c:

·c: ·c: "C "'O

40 40

2oi-_.J....._..J...._...J...__J_--L..l~--'---J 20.___.__.__ ___ ,........._._.____.___.__,

0 10 20 30 40 0.0 0.5 1.0 1.5 2.0

moisture content(%) hygroscopic moisture content(%)

Figs. 10, 11 - Vertical profiles of moisture content and hygroscopic m. c (at R.H. 75%) for drilling series l

431

Drilling Orillin_g_ dej>lh

level 0-8 cm 8-16 cm 16-24 cm

Hygroscopic Sulphates Hygroscopic Sulphates Hygroscopic Sulphates

moist. cont. content moist. cont. content moist. cont. content

_(_cm) (%) (%) i_o;~ 1%1 (%) (%)

100 0.70 - 0.84 - 0.84 -80 0.80 - 0.75 - 0.68 -60 0.68 0.16 0.84 0.13 0.97 0.12

40 0.72 0.17 1.09 0.13 0.98 0.12

20 0.85 0.09 1.15 0.13 0.80 -

Table 2 - Hygroscopic moisture content at R.H. 75% and sulphates content for drilling series 1

3.2 Assessment of the effectiveness of some renderings for the rehabilitation of wet walls The drilling method was carried on repeatedly in the course of time on the same walls (fig. 12) to control the effectiveness of some rendersd proposed as a treatment for rising damp. Four types of renders were applied among which a "macro~ porous" product; the test was applied in order to assess the improvement in evaporation promised by the producer : • Render 1 - a "macro-porous" render with an external layer of finishing based on a "'vapour

permeable" mortar; • Render 2 - only a layer of "macro-porous" render, the same as in render 1, without any

finishing; • Render 3 - hydraulic lime based mortar (for comparison); • Render 4 - cement based mortar with air-agent additive (for comparison). Renders 3 and 4 do not seem to produce any variation of moisture content of the wall, perhaps because moisture content was already low before renders were applied (November '95). Masonry on which is applied Render 2 shows an appreciable decrease in moisture content during the first seven months after its application. Effect of Render 1 does not appear so clearly yet being the moisture content of the wall at first higher and afterwards decreasing again.

3.3 Application of the method to some historic buildings Moisture profiles in brick and tuff masonry are given in the following as examples of real application of the powder drilling method on site. All profiles are the average of 2 or 3 "drilling-lines" within the same wall . In most of the cases shown sampling took place at 2 depths; apart from the actual moisture content (determined with the gravimetric method), also the hygroscopic moisture at 93% R.H. is determined for the same samples. Drying of the samples was done at 40 °C till constant weight. The aim of the drilling was to find some help in diagnosing the causes of the observed damage situation.

Oudewater - Reformed church The samples were drilled at the plint zone of the church and the walls were made of tuff stone. The facade had been treated with a water-repellent and a severe spalling was detected at the treated area together with a loss of bond of the pointing (fi.13a) . The damage was concentrated at the lower part of the wall up to 1. 50m. The drilling samples were taken at 3

432

Render2 Render1

80 80 -- E

E 0 0 -- Q)

Q) ~ 60 ~ 60 O> O> .£ .£ ·;:::: ·;:::: "C "'O 40

40

20 20 0 10 20 30

0 10 20 30

moisture content(%) moisture content(%)

Time

.__._ Nov.94

Render3 - Jun.95 Render4

---- Nov.95 100 100

80 80

- E E 0 0 --Q) Q)

~ 60 ~ 60 O> O>

:§ .£ ·;:::: ·;:::: "C "C

40 40

20'----'-~'----'-~'---91 ...... 20'----'-~..____.____; _____ __.

0 10 20 30 0 10 20

moisture content(%) moisture content (%)

Fig. 12 - Render effect on rehabilitation of wet walls: vertical profiles of moisture content in the course of time

30

position in the SW facade; the results given in fig. l 3a are the average of 3 (fig. 13b ). The measurement were carried out shortly after a rainy period.

Diagnosis: The fact that actual moisture content is hrgher than the hygroscopic at 93% R.H. shows that there is an external source of moisture. The moisture profile over the height and the distribution over the depth indicate a combination of rising damp and rain penetration (moisture content of outer zone -partially- higher than deeper in the wall) . rain water

433

g !: Cl

' ii) .c

2.0

1.8 ----- •d!al(\().10)

-fr- ·- (l!J0.250) 1.6 -+-- !W.93 ... RH (10.70)

~ . 1.4

"( 1.2 :.,

~~ ~ - 0-- hygr.93,.RH (200-250)

1.0 " 0.8 "·i

!" 0.6

9 0.4

0.2 .. . !'

•O

0.0

0 5 10 15 20

moisture content (% m/m)

Fig. 13 - Oudewater, Reformed church. Damage caused by presence of moisture and vertical profiles

penetration is due to lacking pointing and damaged zones. As the hygroscopic content is rather low, salt crystallization was not considered to be the cause of the damage which 1s probably due to the frost action.

Rossum - Church tower (Tuff stone)

25

Drill samples were taken at two position in the S facade where spalling and scaling of the tuff stone were detected; a moist zone was also visible up to 1-1.Sm (see Figl4a) The results given in fig. l 4b are the average of 2. The measurements were performed during a rainy period. Diagnosis: The moisture profile points at rising damp. The moisture content at the surface is almost in all cases higher than deeper in the wall; this is showing the influence of rain. The hygroscopic moisture content is highest between 1 m and I . 5 m, due to the crystallization of salts in that zone.

2.0

1.8

1.6

1.4

I 1.2

~ 1.0 CJ 'iii .c 0.8

0.6

0.4

0.2

0.0

I I ~l

•" I ~ I 0 2 4 6 8 10 12 14 16 18 20

moisture content (% m/m)

Fig. 14 - Rossum - Church tower. Damage caused by presence of moisture and vertical profiles

434

Molenaarsgraaf - Reformed church (Brick masonry) The walls of the church are brick masonries and spalling of the bricks was detected at the lowest zone of the walls (Fig. I Sa) The wall had been treated with a water-repellent. The sampled wall was oriented SISE. The samples were taken at two positions. The results in fig. l Sb are the average of the 2 samples. Diagnosis: The moisture profile shows rising damp, over the full height of the sampling (deeper in the wall) and up to 1 m ca. in the outer zone of the wall. The hygroscopic moisture content is relatively low. Frost action was the most probable cause of the observed damage.

2.0

1.8

1.6

1.4

I 1.2

~ 1.0

~ 0.8

.. " " " .. " ~ .. .. . .

R ..

~

~-- ·j -e- .... , {lOOJOOJ :

-+- .,,,..,.. •• 1<>501 !

~ -<>- ..... .,,. .. i2!1>.J1Xll

~ H

I ~ l

~ l 0.6

0.4

0.2

0.0

+ ~ I =s: I"? ~

I ~ 0 :s ~ ;r i

0 5 10 15 20 25 30 moisture content (% m/m)

Fig. 15 - Molenaarsgraaf - Reformed church. Damage caused by presence of moisture and vertical profiles

4. DISCUSSION OF RESULTS AND CONCLUSIONS

The results of the research carried on in laboratory and on site show that the measurement of moisture content and profile by the drilling method is fairly reliable provided that a calibration of the test is done for every different material tested. The results reliability is influenced and limited by the hardness, porosity and mechanical strength of the tested material. Other influences on the results of the test are given by the adopted method of application and by the equipment as follows: Influence of the drill speed: low speed (method B) is preferred for hard materials (sandstones, granites, etc. Influence of reference unit: method B gives the best results both on tuff and bricks; unfortunately the test was not carried on the sandstone. The best results differs from the bulk moisture content of about ± 2.5 % when, according to BRE document [l], the percentage should have been ± 1 % for tender materials like mortar and softmud bricks. Calcium-carbide method: ref. method B gives more reliable results. For the data obtained at Politecnico and BRE the moisture content is always higher than the one determined by the gravimetric method. Apparently at TNO lower values were obtained. On site full-scale models: an acceptable repeatibility of the results was obtained. The method did not show a good efficacy in the determination of hygroscopicity values probably due to the detection of the moisture content at 75 % R.H instead of 93%. The contemporary possibility of determining the salt content allows also for a better diagnosis of the eventual decay of the wall.

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Application to real buildings: powder drilling in combination with the determination of the hygroscopic behaviour of the same samples is a useful method: • to assess whether an external moisture source does exist; • to assess the source of moisture (rising damp, rain, hygroscopicity); • to have an indication of presence of salts (if the hygroscopic behaviour is determinated at

93% the indication for the presence of salts may be considered quite good); • to diagnose the damage and to propose measures. Limits of the method on site are: • inhomogenous structure of walls: mortar vs. brick/stone, or varying quality of bricks; • 3 positions of sampling are considered necessary in order to reach a reliable results.

AKNOLEDGEMENT

Authors wish to thank M . Antico and G. Ghilardi for their collaboration in the experimental work, S. Gaggioli, G. Moretti, A. Scaglia and S. Triulzi for data collection and elaboration.

REFERENCES

[1) Newman, A.J. , Improvement of the drilling method for the determination in building materials, BRE Current Paper CP 22/75, in RILEM Document MS93/1 5 [2] NL Standard NEN 2778, Moisture Control in Buildings. Determination methods [3) De Wit, M .H. , Schellen, H.L. , Pel, L. , Measuring methods of moisture in solids, Didactic Seminar on Rising Damp in Masonry, CNR-PFEd, Bari, 17-18 September 1991 [4] G. Baronio, L. Binda, F. Cantoni, E. Carraro, E .D. Ferrieri, P. Rocca, T. Squarcina, Full-scale models as on site laboratories, EC Worshop "Research on the conseFVation of brick masonry monuments", Environment Programme, Leuven, 24-26 October 1994 [5] BRE, Rising damp in walls: diagnosis and treatment, Digest 245