Use of salt solutions for assuring constant relative humidity
Contents
1. LES European Union EM Governo da Rep blica Portuguesa Regarding the readings of the sensors the most stable was the one from Vaisala Its readings are useful as a reference to compare the readings of the other sensors Usually the behaviour of the sensors is as follows Sensirion SHT71 gives the highest values and the lowest values are given by Honeywell sensors HIH4010 Sensirion SHT21 readings are in the middle Finally in regard to the use of the cooking salt the readings have shown that is feasible to achieve a constant relative humidity with this kind of solution This is an important conclusion in view of establishing low cost solutions for moisture control and testing of cement based materials 5 2 Measurements for the containers with the same NaCl salt The readings of the sensor in each container are shown in Fig 27 to Fig 31 In these experiments the NaCl salt is used in the solution and the influence of the quantity of salt in humidity control is to be assessed The reference value is RH 7596 according to Vaisala s relative humidity calibrator After the glass of water is placed in containers 1 to 4 at the age of 7 days the measurements continued from then on Container 1 20 gr NaCl 10 23 gr H20 Glass of water inside 00 Ul 9 SHT21 N Un B SHT71 ES gt S E 3 lt U a 42 XU U ecc N O 300 Time hours Fig 27 Relative humidity readings in container 1 solut2. 2 2 General outline basic principle and procedure eee 17 2 2 1 Test with different salts eessssseennesesssseeerrsssssssrrerssssssserrresssssserrreessssseerrressssseene 17 4 1 2 Test with the same salt NaCl ccccccsscccesecscesececeeecseeeceeenssseesceseeeceseueseteueceeensss 20 a ARE SUMING ANO SCU O aea E o nen ai E E EE 21 5 1 Measurements for the containers with different salts ccc seen 21 5 2 Measurements for the containers with the same NaCl salt eeessseeeeeeeeeee 25 5 3 Water loss from the glasses placed inside the containers eeeeeeen 30 O 2016 09 6 9 are eee etree ee er en ee ee eee er E ee a nt eee da 31 EE i a ts 32 LES European Union EM Governo da Rep blica Portuguesa 1 Introduction To obtain a relationship between moisture loss and shrinkage in concrete structures it is necessary to determine the moisture profile in concrete along time Regarding internal moisture content in concrete there are several measurement methods mostly based on the measurement of internal water concentration and on relative humidity According to the objectives of the project both kinds of methods will be used Many samples and tests have to be done before obtaining reliable results One of the main issues that influence moisture profiles in concrete samples is related to the environmental conditions to which the s
3. Data taker DT515 and CEM20 expansion module Fig 11a shows the wire scheme for Honeywell sensors and Fig 11b shows the wires already connected with a Honeywell 4010 sensor Supply Voltage 5 V HIH 40XX VOLTAGE OUT Minimum Es European Union EM Governo da Rep blica Portuguesa a b Fig 11 a Wire scheme of Honeywell sensors b wires installed on the sensor 1 2 Preliminary sensor testing Before the beginning of the experimental program envisaged in this report test of salt solution performance in order to assure constant humidity conditions the sensors were exposed to controlled environmental conditions to compare differences between them and check the accuracy of the readings The 4 types of sensors mentioned in Section 3 1 Sensirion SHT21 Sensirion SHT71 Vaisala and Honeywell HIH4000 4010 were placed in the controlled chamber at 60 RH and 20 C Fig 12 shows the readings during a period of 48 hours starting 2 hours after the sensor s installation As it is observed the measurements were close to the target value of 6096 RH given by the climatic room The range of the sensors goes from 58 696RH for Vaisala sensor to 65 4596RH for Sensirion SHT71 Considering the accuracy for Sensirion SHT71 of 1 8 RH and for Vaisala of 2 an average relative humidity in the climatic room could be considered as 62 RH considering also the accuracy of Sensirion SHT21 and Honeywell HIH4010 After this test the sensors
4. H4 software window sensors are displayed in different colours Es European Union EM Governo da Rep blica Portuguesa 3 1 2 Vaisala sensor The Vaisala sensor HM44 has been designed specially to measure relative humidity inside concrete see Fig 7 This sensor operates with an analogue signal instead of digital but the measure principle is the same as Sensirion sensors which is a capacitive sensor The measurement range for relative humidity is from O to 100 RH with an accuracy of 296 RH for O to 9096 RH and 396 RH for 90 to 10096 RH The response time is 15 seconds that is lower than in Sensirion sensors c Fig 7 a Vaisala s HM44 sensor b Data logger c Kit for measuring RH inside concrete For measurements in fresh concrete the procedure is as follows e First a hole is bored at the required depth cleaned out and a plastic sleeve is inserted Es European Union EM Governo da Rep blica Portuguesa e The probe is inserted into the sleeve and sealed The material at the bottom of the hole releases humidity into the space around the probe until the equilibrium is reached e When the humidity in the hole has reached equilibrium the probe is inserted and left to stabilize for a short time before a reading is taken 1 1 1 Honeywell sensors The Honeywell sensors HIH 4000 and HIH4010 have been used on this experiment see Fig 8 These sensors have a nearly linear voltage output in regard to moistur
5. Test with different salts The salts solutions were placed in each of the 5 containers and the latter were left undisturbed for 24 hours for the salts to stabilize according to Vaisala s calibrator user manual The comparison between the sensors is also a target in this experiment so different sensors were placed in each container see Fig 17 Table 4 indicates the sensors that were placed in each container Fig 17 Sensors ready to place inside the containers Table 4 Sensors used for each container with different salts Container sensos S 2 SensiionSHT21SensionSHT71 83 Sensirion SHT21 Sensirion SHT71 04 Sensirion SHT21 Sensirion SHT71 5 Honeywell HIH 4010 004 Vaisala To place the sensors in the containers without affecting the internal environment every hole or opening for passing the wiring has to be sealed In this case tape was used to seal the gap between Es European Union EM Governo da Rep blica Portuguesa the cap and the container After pouring the salt solutions waiting 24 hours for their stabilization and installing the sensors a period of 2 hours was necessary to allow the sensors to stabilize and start taking the measurements Fig 18 Final distribution of the containers and the installed sensors After pouring the salt solutions wait 24 hours for their stabilization and install the sensors a period of two hours was necessary to leave the sensors to stabilize and start
6. really change the tendency to give readings near 75 RH However the influence of the amount of salt solutions is clear in regard to the stability of the container RH after the water glass is placed inside The higher the amount of salt solution the smaller the difference between the sensor readings Hence containers 3 and 4 40gr and 50gr of NaCl respectively showed more stability in the readings before placing the glass of water and a small difference between the readings of relative humidity after that Container 5 revealed stable readings during 500 hours 21 days being able to maintain the relative humidity which confirms the feasibility of using cooking salt as an agent to create controlled relative humidity LES European Union EM Governo da Rep blica Portuguesa 5 3 Water loss from the glasses placed inside the containers While checking the stability of the salts solutions and the influence of the glass of water for the relative humidity measurements the loss of water from the glasses was monitored as well through regular weighing It is important to note that this kind of monitoring considering the limitations of the containers and the climatic room could not be as frequent as for the RH measurements Water loss through evaporation occurs associated to three main factors environmental relative humidity temperature and wind speed Handling the glass opening the container to take out the glass waiting and placing t
7. that are commercially available and salt compositions that were not specifically designed for environmental control it was possible to create constant relative humidity conditions along time Different values of relative humidity could be reached and the performance of the salt could be analysed At the same time it has been of relevance to compare and to check the RH sensors performance to allow appropriate decisions about the type of sensor more suitable for particular targets in the future either inside laboratory or for in field applications Reaching stability of sensor readings at low and at high RH values was difficult because of the salt solutions stability and of the accuracy of the sensors at these extremes It is common that RH sensors have limitations reaching relative humidity below or near 10 RH and above 90 RH as it was observed on the readings for the salt solutions used Regarding the salt solutions as larger the container the more salt would be necessary to reach a stable environment A good practice or visual technique to achieve this is to cover the base of the container with at least 3 mm of salt in the proportion which is required to obtain certain relative humidity LES European Union EM Governo da Rep blica Portuguesa As it was showed in the results for the containers with cooking salt it is feasible to achieve constant RH with this kind of salt This opens the possibility to create homemade contr
8. the disturbance to the experiment caused by opening the container and weighing the glass of water In fact the operation has to be relatively fast and the container should be kept air tight while the glass is being weighed Fig 21 shows the glasses placed in containers 1 to 4 Fig 21 Glasses placed in containers 1 to 4 The relative humidity measurements continued after the water glasses were placed in the containers The idea was that ideally the stability of the environment created by the salt solutions should not be affected because of the glass of water inside 4 1 2 Test with the same salt NaCl For this group of containers the procedure was similar to the first one with the difference that only Sensirion sensors were placed simultaneously in 1 to 4 containers and only a Vaisala sensor was used in container 5 see Table 6 Table 6 Sensors used for each container with the NaCl salt Es European Union EM Governo da Rep blica Portuguesa Containers with equal salt Container Sensors Sensirion SHT21 Sensirion SHT71 2 jSensrionSHT21 SensiionSHT7l 3 jSensrionSHT21 SensiionSHT71 4 jSensrionSHT21 SensiionSHT71 O 5 asia S 5 Results and discussion 5 1 Measurements for the containers with different salts The readings of the sensors in each container are shown in Figures 21 to 25 The objective is to monitor the behaviour of the salts along the time to compare the readings of e
9. FCT Funda o para a Ci ncia e a Tecnologia COMP ET E MINIST RIO DA CI NCIA TECNOLOGIA E ENSINO SUPERIOR PROJETOS DE INVESTIGA O CIENT FICA E DESENVOLVIMENTO TECNOL GICO RELAT RIO REFERENTE AO PROJETO PTDC ECM 099250 2008 Comportamento em servi o de estruturas de bet o uma abordagem multi f sica das tens es auto induzidas Use of salt solutions for assuring constant relative humidity conditions in contained environments Autores Gonzalo Quincot Miguel Azenha Joaquim Barros Rui Faria Guimar es UM 2011 E23 Uni o Europeia Fundos Estruturais EM Governo da Rep blica Portuguesa Content UEM MOCO UON ROTE RE RD N ARE E O E 3 2 Salt solutions for humidity calibrators esses nnne 4 3 Equipment to measure temperature and relative humidity eee 5 3 1 Vale SO ne Y CENE 5 1 2 Preliminary sensor testing ssesressesresreeseeresrresrersenresrresrerserresreesseresrresreessereesresreeseeresns 12 2 POMO OE a e lho itum IPM dai Saci ii P ted rws e Grass ON UM MU e Deis ME 13 2 1 Environmental moisture control in containers cccccesseecccceseeeecccceseusecccessueeeeeessaaaeeees 13 2 1 1 OTM o ph c HU RN 13 2 1 2 Testing NGS AICS rasto diana aan rbada sai aue USER dida os hi paia a di ado insane a 13 2 1 3 Preparing the salt SOLUTIONS ssa sessiasarsiosasiosesiists poo en rkk ee kx ER Drew err Ex dada Ov EE SE ERR 15
10. ach sensor for each salt solution and to check the influence of the containers volume on the RH measurements based on the reference values according to the Vaisala s relative humidity calibrator Container 1 NaCl H20 7596 RH pao a dup SHT21 2 1 V Y Oa AY ev AMA NS TTC o Met vi E AAA AMA ARM TA xx x amp xx BASS S x x x x A HIH 4010 004 Relative humidity 96 X Vaisala 200 300 Time hours Fig 22 Relative humidity readings in container 1 expected relative humidity of 75 E European Union EM Governo da Rep blica Portuguesa Container 2 LiCl H20 11 RH N UI N O 9 SHT21 M SHT71 pa Un 53 2 E 3 lt U gt dud amp U cc A HIH 4010 004 pa e 200 300 Time hours Fig 23 Relative humidity readings in container 2 expected relative humidity of 1196 Container 3 MgCl2 H20 3396 RH IA 9 SHT21 UJ Ul B SHT71 Relative humidity 96 UJ A HIH 4010 004 200 300 Time hours Es European Union EM Governo da Rep blica Portuguesa Fig 24 Relative humidity readings in container 3 expected relative humidity of 33 Container 4 K2SO4 H20 97 96 RH SHT21 B SHT71 S 2 E 3 lt U gt ded ic U cc A HIH 4010 004 200 300 Time hours Fig 25 Relative humidity readings in container 1 expected relative humidity of 9796 Es European Union EM Govern
11. at 100 105 C and less than 5 RH for 10 hours Then Re Hydration at 20 30 C and 7596RH for 12 hours John Newman 2003 Es European Union EM Governo da Rep blica Portuguesa 100 c co Normal Range ha R oc o Relative Humidity 1 A 20 20 40 60 80 100 120 Temperature C Fig 3 Operating conditions for the SHT21 sensor Sensirion sensor SHT71 is shown in Fig 4 This model has similar characteristics to the SHT21 one except for the fact that it has higher accuracy 1 8 RH being more expensive as well Fig 4 Sensirion sensor SHT71 The operating conditions are similar as for SHT21 but the normal range is higher until 9596RH as shown in Fig 5 LES European Union EM Governo da Rep blica Portuguesa 100 Relative Humidity 75 S 40 20 0 20 40 60 80 100 120 Temperature C Fig 5 Operating conditions for the SHT71 sensor The experimental set up and the interface of the software for Sensirion sensors are shown in Fig 6 The data logger has 4 channels which is connected to a computer with the data logging software SS O zjni x Fie Helo EK H4 Viewer V1 O SENSIRION Daa Handing Aeshi Hundes Stat hzc Foto Tamparan Interes 1 at E n zi Molan Hmm 204 Bo 2 Relativa Humidity Temperature Frodedras Horn Temperature a b Fig 6 a Schematic evaluation kit EK H4 for Sensirion system b EK
12. d in each container but in different quantities Fig 16 shows the containers numbered from left to right Both groups respect the same order The proportions for the salt solutions and the expected relative humidity were presented in Table 1 The quantities actually used in the containers are reproduced in Table 2 and in Table 3 and fulfil the target values of Table 1 for each expectable relative humidity E European Union E Governo da Rep blica Portuguesa P d MAL fA LILI JD 320 m C Fig 16 Containers numbered from left to right The proportions and the expected relative humidity were shown in table Table 1 The quantities used in the containers are shown in the table Table 2 and Table 3 The proportion remains respect to the values showed in table 1 for each expectable relative humidity Table 2 Proportions for the salt solutions used in the containers different salts Container Sat Salt content g Water Content g Expected relative humidity 1 75 2 u 533 sea am 3 moa 533 546 88H 4 Kso 533 1819 9m 5 jCookingSalt NaC 5333 27283 7596 Table 3 Proportions for the NaCl solutions used in the containers 1 na 20 102 7596 02 03 a o Cooking Salt NaCl Es European Union Governo da Rep blica Portuguesa 2 2 General outline basic principle and procedure 2 2 1
13. e variations The input current is 5V and each individual sensor has a calibration data sheet available see Fig 9 Fig 8 Honeywell sensors HIH4000 and HIH4010 series 003 and 004 from left to right Mode HIH 4000 003 A Came s2 Z4 Wafer 0309M MRP ama O Calculated values at 5 V Vour at 096 RH 0 826 V Vour at 75 396 RH 3 198 V Linear output for 3 596 RH accuracy at 25 C Zero offset 0 826 V Slope 31 483 mV RH RH Vour Zero offset slope Vour 0 826 0 0315 Ratiometric response for 096 RH to 10096 RH Vour VsuppLy 0 1652 to 0 7952 LES European Union EM Governo da Rep blica Portuguesa Fig 9 Example of data calibration printout The HIH4000 and HIH4010 sensors have an accuracy of 3 5 in a humidity range from 0 to 100 The response time is 15 seconds for the HIH4000 sensor and 5 seconds in the case of HIH4010 The supply voltage range varies from 4V to 5 8V for HIH4000 and 2V to 5V in the case of HIH4010 The operating temperature range is from 40 C to 85 C Data collection from the Honeywell sensors can be made with a general purpose data logger with capacity to measure potential in V In the case of this research a Data Taker DT515 see Fig 10 together with a CEM20 expansion module was used with a total of 30 measuring channels The interface used for these sensors is called DeLogger which belongs to the Data taker suite Fig 10
14. ensor which is usually related with the price as well Each equipment has its calibration sheet and user manual to refine the readings LES European Union EM Governo da Rep blica Portuguesa 3 1 1 Sensirion sensors The Sensirion sensors SHT21 and SHT71 were used in this experiment These sensors are fully calibrated every sensor is individually calibrated and tested have low power consumption long term stability and digital output which is measured through the Sensirion Evaluation Kit EK H4 Sensirion sensor SHT21 is shown in Fig 2 this model does not come with a pin connector so the connectors were adapted by the company as a request at the moment of purchasing the equipment Fig 2 Sensirion sensor SHT21 The accuracy of the sensors is 3 RH with a response time of 8 seconds the time that the sensor takes recognize and read changes in the RH Regarding the operating conditions the sensor works stable within the recommended normal range reproduced in Fig 3 According to the manufacturer long term exposures to conditions outside the normal range especially at humidity higher than 90 RH may temporary offset the RH signal 3 RH after 60 hours After return to normal range the sensors slowly returns to normal behaviour and response time according to the Sensirion SHT21 data sheet A reconditioning procedure may be used to accelerate the elimination of the offset The procedure is as follows baking in the oven
15. he cup outside until the weighing is finished will change the three mentioned factors This can affect the results superimposing the loss of water due to the salt solution and the one due to the environmental exposure For each container Fig 32 shows the loss of water mass from the glasses 4 Container 1 EB Container 2 A Container 3 im o0 w 9 Sm 2 74 O im U X Container 4 200 300 Time hours Fig 32 Loss of water in the glasses inside the containers LES European Union EM Governo da Rep blica Portuguesa The loss of water is small during the first day of placement After 2 days the loose of water is higher because of the solutions adsorption Finally the loss of water decreases because the salts finish the adsorption process Even with differences in the loose of water and in the behaviour of each solution in 16 days 3 3 gr have been lost in the container with more amount of salt with a tendency to decrease the loose as the salt solutions stabilize The same for the other containers According to the measurements if a concrete specimen is placed inside the containers can be predicted that the loss of moisture will not be affected significantly by the salt solution 6 Conclusions On the present experiments the possibility of creating controlled environmental conditions using salt solutions in simple containers was studied with favourable results Using simple containers
16. ion for 20 gr of NaCl LES European Union EM Governo da Rep blica Portuguesa Container 2 30 gr NaCl 15 35 gr H20 Glass of water inside tly Ur SOREnCt Re L2 9 SHT21 B SHT71 S 2 z o E 3 lt U gt dud amp U cc 300 Time hours Fig 28 Relative humidity readings in container 2 solution for 30 gr of NaCl Es European Union EM Governo da Rep blica Portuguesa Container 3 40 gr NaCl 20 46 gr H20 Glass of water inside do A SHT21 B SHT71 53 2 E 3 lt U gt ded T U ecc 300 Time hours Fig 29 Relative humidity readings in container 3 solution for 40 gr of NaCl Es European Union EM Governo da Rep blica Portuguesa Container 4 50 gr NaCl 25 58 gr H20 Glass of water inside SHT21 N Un B SHT71 S 2 o E 3 lt U gt ded amp U cc 300 Time hours Fig 30 Relative humidity readings in container 4 solution for 50 gr of NaCl Es European Union EM Governo da Rep blica Portuguesa Container 5 30 gr NaCl cooking salt 15 35 gr H2O N Un N O o Un B Vaisala Ss gt E I en 2 ded 2 U c leu Ul Ul Ul 300 Time hours Fig 31 Relative humidity readings in container 5 solution for 30 gr of NaCl cooking salt All the containers could give values near to the expected relative humidity of 75 and the quantity of salt solution did not
17. midity in the Vaisala s calibrator Sat Water content Expected relative humidity 15g LiCl 30gMgCI2 3ml am 20g Nac 30g K2504 According to these proportions the same salts solutions were poured in the containers expecting to obtain relative humidity values close to those ones established in Vaisala s calibrator The effect of the amount of salt used in each container was also checked 3 Equipment to measure temperature and relative humidity 3 1 Measuring systems The measurements were done with three different brands of sensors Sensirion Vaisala and Honeywell These sensors where chosen as they have a relatively low cost and are commercially available The shape of these kind of sensors allow them to be easily inserted in concrete which is the chosen procedure to measure relative humidity at different depths All these sensors have the same measurement principle based on capacitance Capacitive sensors consist of a thin layer of water absorbent polymeric or inorganic material that is coated onto a conductive base This layer is then covered with porous conductive layer material With the increase of the relative humidity the water content of the polymer increases too Physics 2010 The capacitance is measured by the variation of an AC signal across the sensor and this change is transferred to a RH value This kind of system may be connected to a data logger The precision depends of the technology of the s
18. o da Rep blica Portuguesa Container 5 NaCl cooking salt H20 N Ul BERN zd d ae adt N O HIH 4010 004 ep Un B Vaisala Ss gt 2 E 3 I en 2 dud Er q c leu O UI Un Ul 200 300 Time hours Fig 26 Relative humidity readings in container 5 expected relative humidity of 75 These figures show that it was feasible to achieve the expected relative humidity considering that the salts could not be 100 efficient and the limited accuracy of the RH sensors The readings show that the less stable salt solution was K2SO4 however according to the RH sensors data sheet sensors can give readings with not enough accuracy at RH values of more than 90 as shown in section 3 1 In this case the relative humidity to achieve for the solution with K2SOA is 97 Another issue is that even if the sensors can reach those values of relative humidity more than 90 they take relatively long times to attain moisture equilibrium with the environment That is why an initial increase of the values of RH can be seen at the beginning of the readings This is attributable to the sensor performance and not to actual RH changes inside the container For the salt LiCl solution the expected relative humidity is 11 The efficiency to obtain this RH value that the salt could get at this range influence the readings obtaining values from 1 to 2 higher than the expectable as is shown in Fig 24
19. olled environments when there are no other resources Finally the glasses of water placed inside the containers made the relative humidity values to increase but with a smaller variation in the case of the containers with more quantity of salt solution This shows that this effect can even disappear or be disregarded putting a higher amount of salt solution to control and reach certain relative humidity After this approach the objective of creating a controlled environment for concrete or porous material specimens to analyse the loss of moisture shrinkage or any other phenomena requiring known environmental conditions has been achieved in an economical way The testing of concrete specimens subject to different relative humidity in a controlled environment will be feasible with a wide range of options that consider volume size of the specimen and a specific value of relative humidity 7 References John Newman B S C 2003 Advanced Concrete Technology Concrete Properties Butterworth Heinemann 1 5 11 Physics C 2010 Relative humidity sensors 1 3 LES European Union EM Governo da Rep blica Portuguesa
20. pecimens are subjected e g humidity temperature wind speed For a proper characterization of the influence of environmental conditions on moisture losses such conditions have to be known and stable The experiments initially envisaged in the scope of this project aim to have constant temperature relative humidity and wind speed throughout the whole testing period The experiments described in this report have the intention of creating known environmental conditions in containers where the samples and specimens are to be tested Such conditions are relatively easy to achieve through the use of climatic cnambers However the number of climatic chambers is usually limited in laboratories and the climatic conditions are not always suitable for the experiments conducted by the several researchers of the laboratory With this limitation in view it was decided to test the possibility of assuring constant humidity conditions inside plastic containers through the use of salt solutions usually applied in calibration of humidity sensors The intention is to have several testing humidities inside a climatic chamber that just needs to control temperature much cheaper than humidity control In the scope of this report a walk in climatic cnamber with 20 C 0 2 C and RH 60 3 is used To achieve the necessary conditions salt solutions with a known target relative humidity according to their use in humidity sensor calibration in Vaisala s use
21. r manual were placed in closed containers where specimens will expectably be placed for testing The humidity inside the containers was continuously monitored through the use of several types of humidity sensors thus LES European Union EM Governo da Rep blica Portuguesa allowing to relate the salt solution efficiency in view of the targeted relative humidity in the container and its stability along time Conclusions are withdrawn in regard to the behaviour of the tested types of humidity sensors 2 Salt solutions for humidity calibrators Vaisala is a company that sells relative humidity sensors among other measurement equipment In the scope of this project the Vaisala humidity calibrator HMK15 see Fig 1 was purchased together with the Vaisala HM44 set for measuring humidity in concrete P EE la B Sa A C Ad 7 A L s gt wae Fig 1 Vaisala HMK 15 relative humidity calibrator The HMK15 calibrator is based on known relative humidity being assured by salt solutions for a specific chamber volume of 20 cm diameter 5 cm height 3 5 cm The salts used in the calibrator are Lithium chloride LiCl Magnesium chloride MgCl2 Sodium chloride NaCl and Potassium sulphate K2SO4 The salt solution and the expected relative humidity values in the chamber are shown in Table 1 Es European Union EM Governo da Rep blica Portuguesa Table 1 Salt solutions and expected relative hu
22. s used for environmental control in the containers Before starting the experiments the chemical reaction of the salts had to be evaluated see Fig 13 Different salts have different chemical reactions and some of them can be dangerous In this case the LiCl the MgCl2 and K2SO4 are known to have aggressive reactions with water according to Vaisala s Calibrator user guide Especially Lithium chloride that is very corrosive and can easily cause skin burn Sodium chloride and the cooking salt were not tested because the behaviour is known Fig 15 Corrosive salts safety testing European Union Governo da Rep blica Portuguesa The salts were placed with care and without skin contact in a glass slab and leaved there for 5 minutes to stabilize with the environment Then small amounts of water were poured in each salt Magnesium chloride MgCl2 and Potassium sulphate K2SO4 did not present aggressive reaction when the water was poured Lithium chloride LiCl presented a high heat release which can be really corrosive if enters in contact with skin Based on this test the heat release of Lithium chloride reaction with water last between 6 to 8 minutes 2 1 3 Preparing the salt solutions The salt solutions were used to obtain different relative humidity values in each container Two groups of 5 containers each were used In one group different salts in the same quantity were used In the second group the same NaCl salt was use
23. taking the measurements At day 7 a glass of water was placed in each container to represent an extreme case of fully saturation enforcing a great disruption to the moisture balance due to significant evaporation The glass was placed on top of a suitable base Fig 20 to prevent the glass from being wet by the salt solution thus ensuring the mass loss of water to be uniquely associated to evaporation The objective was to check if the salt solution in the container was able to absorb the significant increase of relative humidity induced by evaporation of the water in the glass and how it affects the effectiveness of the salt solution and its capacity to maintain the intended relative humidity in the container Es European Union EM Governo da Rep blica Portuguesa Fig 19 Glass and base to be put inside the containers Different amounts of water were poured and weighed in 4 glasses one for each container using a high precision weight scale that was installed in the climatic room Fig 20 Table 5 reproduces the initial glass of water weights for the experiments Fig 20 Weighing a glass of water in a high precision weight scale Table 5 Glass of water content for each container Es European Union EM Governo da Rep blica Portuguesa Glass of water content gr 44 23 o2 45 99 3 mo a a Upon placement in the containers the glasses of water were weighed regularly Care was taken to minimize
24. were ready to start the measurements Environmental Conditions bes rer EE EY Y Y YE E YY B SHT71 A Honeywell 8 gt do o E I U 2 dud fU U ec X Vaisala 20 30 Time hours LES European Union Governo da Rep blica Portuguesa Fig 12 Readings for environmental conditions 2 Experimental program 2 1 Environmental moisture control in containers 2 1 1 Containers Controlling the environmental conditions for the cement paste mortar concrete specimens is an important issue Fig 13 shows the dimensions of the containers used for the specimens Fig 13 Containers dimensions 2 1 2 Testing the salts The environmental moisture control in the containers was achieved through the use of salt solutions as referred before As the volume of the used containers is different from the one in the calibrator chamber by Vaisala mentioned in Section 3 1 different proportions of salt were tested The salts from Vaisala s calibrator are expensive hence a local store of chemical products was chosen to order the same salts Lithium chloride LiCl Magnesium chloride MgCl2 Sodium chloride NaCl and Potassium sulphate K2SO4 were purchased and common cooking salt NaCl was purchased as well to compare the behaviour against the Sodium chloride The flasks containing the salts used in this experiment can be seen in Fig 14 Es European Union EM Governo da Rep blica Portuguesa Fig 14 Salt
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