Method for Evaluation of Concrete Permeability

1 Method for Evaluation of Concrete Permeability Valdir Moraes Pereira 1. Gladis Camarini 2. ABSTRACT. Permeability of cement based-materials is the principal factor that provides their durability. This kind of test is an important parameter for estimate their service life. Several Concrete Permeability tests has been realized to try to measure and understand the movements of fluids in Concrete porous and to associate it with its durability. In this context, Thenoz Method has demonstrated satisfactory results when measuring air Permeability of Concrete . Thus, the aim of this work is to evaluate Thenoz methodology, measuring outflow velocity and Reynolds number during air Permeability tests of Concrete . In this way, Concrete specimens were produced and submitted to two curing conditions (in water and at laboratory conditions). The specimens were tested at 14 days, 28 days and 350 days.

2 Results obtained have shown that Thenoz methodology is efficient and an economical Method for measuring air Permeability of Concrete . Concrete age and curing conditions influenced air Permeability results. The Method used shows that outflow regime can be considerate as laminar, in accordance Reynolds number obtained in this study. KEYWORDS. Concrete , Air Permeability , Thenoz Method , Reynolds number. 1. Faculty of Civil Engineering, Architecture and Urban Design, State University of Campinas (FEC-UNICAMP), Campinas, S o Paulo, BRAZIL, 2. Faculty of Civil Engineering, Architecture and Urban Design, State University of Campinas (FEC-UNICAMP), Campinas, S o Paulo, BRAZIL, Valdir Moraes Pereira and Gladis Camarini 1 INTRODUCTION. Permeability of cement-based materials has been seen as the main responsible for its durability because it controls the movement rate of aggressive ions inside Concrete and may cause its physical/chemical degradation.

3 So, several approaches have been proposed to evaluate this Concrete property, having as main goal the search for an effective, viable and economic methodology to measure and describe air Permeability of Concrete [PERRATON, 1989; SONG & NWON, 2007]. Discrepancies found in Concrete Permeability results may occur due to many factors such as inadequate mathematical equations or methodology employed where results obtained cannot correspond to physicals phenomena really involved. Mathematic equation cannot take in account some physical phenomena and presents mathematical inadequacy to the type of flow mechanisms measured. Therefore, for Permeability tests apparatus and proposed methodologies have been proven to be sought not only to evaluate the Permeability of these materials, but the credibility and validation of the test apparatus employed [GARDNER et al.]

4 2008]. Thus, some factors may be employed for measuring the validation of results for Concrete air Permeability : Reynolds number (Re) is one of them. Permeability results can not be realistic due type of fluids movement into porous media, where fluids which flow in high velocities can entail pressure drop, causing flow turbulence and generate deviations in Darcy's law. These phenomena can generate results that cannot be real. One way of assessing the fluid turbulence in outflow can be achieved by Reynolds number measurement. Reynolds, analyzing the behavior of an ink filet inside water flow, observed that when flow velocity was low, the ink fillet disposed of in a macroscopically organized way and parallel to the tube. By the other hand, when the flow velocity was increased, fluid molecules movement was totally random [VENNARD, 1966; ROMA, 2006].

5 Thus, Reynolds characterized these types of outflow in accordance three numbers, that after, came to be called by his name: Reynolds number. The three types of outflow, at tubes, were classified, as follows. Laminar flow regime: characterized by Reynolds number lower than 2100 (Re < 2100);. Transition flow regime: this flow type is characterized by a region of uncertainty where there is a transition from laminar to turbulent flow. This flow type can be characterized by Reynolds number between 2100 and 4000 (2100 < Re < 4000). Turbulent flow regime: this phase can be observed for Reynolds numbers above 4000 (Re >. 4000). Among methodologies employed to measure Concrete air Permeability there is the Thenoz Method [THENOZ, 1989]. This Method has shown good applicability in this kind of material. Initially, it has been developed to determine the rocks Permeability and it was based in Darcy's law equation to calculate air Permeability values.

6 However, in order to prove the credibility of the Thenoz methodology used in Concrete , some analysis must be conducted to assess the flow mechanisms provided by this Method . Thenoz Method employs Darcy's law to describe physically and to measure Concrete air Permeability . However, some considerations may be realized when mathematics equations based in Darcy's law are employed, as follows [BANTHIA & MINDESS, 1989]. Pressure inside of porous material caused by fluid movement must be disregarded;. Fluid compressibility on triaxial stress may be ignored;. Outflow regime must considered as laminar;. Temperature effects also must be neglected. 2 XII DBMC, Porto, PORTUGAL, 2011. Method forEevaluation of Concrete Permeability The aim of this work was to determine outflow regime occurred during the test of Concrete air Permeability by Thenoz Method . It was observed the results of air flow velocity into Concrete porous, which is necessary to determine Reynolds number of outflow.

7 Thus, it were possible to evaluate Thenoz Method to measure Concrete air Permeability , and also to determine if air flow into Concrete porous occurred in laminar or turbulent regime as observed by Banthia & Mindess [1989]. 2 EXPERIMENTAL PROCEDURES. Materials used in this experimental work were: blastfurnace slag Portland cement named CPIII 40. according to Brazilian standards and Type IS according to ASTM, river sand and crushed stone. Their properties are shown in Table 1. Concrete specimens and mixtures used are shown in Table 2. Concrete specimens were cast in cylindrical molds (100 mm diameter and 200 mm height). They remained in molds for 24 hours and after they were demolded and remained in laboratory conditions (LC temperature of 23 C and 60% of relative humidity), and in water (IC immersed curing) until the age of the tests. These specimens were cut and a slice of with 100 mm diameter and 50 mm height (Figure 1) was used for air Permeability tests (Figure 2).

8 Air Permeability tests were carried out in Concrete at the ages of 14, 28 and 350 days (Table 2). Table 1. Materials properties. Material Properties Fineness (%retained sieve # 200) ..5,8. Blaine (cm2/g)..682,63. Cement CP III 40 (Brazilian Specific Gravity (g/cm3) ..2,99. Standards) Initial Setting Time (h:min) ..2:57. Final Setting time (h:min) .. 4:37. Normal Consistency (w/c ratio) ..0,31. Fineness Modulus .. 2,53. Maximum Size (mm) ..2,40. Fine aggregate Specific Gravity (g/cm3) ..2,60. Bulk Weight (g/cm3) .. 1,43. Fineness Modulus .. Maximum Size (mm) ..19,0. Coarse Aggregate Specific Gravity (g/cm3) ..2,99. Bulk Weight (g/cm3) .. 1,52. Table 2. Concrete specimens, mixtures and curing conditions. Name w/c ratio Age Mix proportion (c:s:cs)* Curing process LC1 0,50 7-28-350 1:2:3 Laboratory conditions (LC). LC2 0,46 7-28-350 1:2:3 LC. LC3 0,42 7-28-350 1:2:3 LC.

9 IC1 0,50 7-28-350 1:2:3 Immerse curing (IC). IC2 0,46 7-28-350 1:2:3 IC. IC3 0,42 7-28-350 1:2:3 IC. *c=cement; s = sand; cs=crushed stone. XII DBMC, Porto, PORTUGAL, 2011 3. Valdir Moraes Pereira and Gladis Camarini Before the test, specimens were 24 hours oven dried at 80 C in order to eliminate the water inside the porous of Concrete . After that, Concrete specimens had their lateral surface sealed. This makes the air flow only uniaxial and perpendicular to cross sectional area of the specimens. All the results presented in this paper were an average of four (4) specimens for each curing condition and age. Figure 1. Preparation of Concrete specimens to air Permeability tests. Sample (50 x 100) mm O' ring Pump Valve Measurement Scale Capillary Tube Level 0. Constant Water Level Figure 2. Scheme of air Permeability apparatus. 3 RESULTS AND DISCUSSION.

10 Air Permeability Air Permeability of Concrete results was obtained according to Thenoz methodology. The calculus was made according to Equation 1. s h0 l k= .. ln ..g S h1 t Equation 1. 4 XII DBMC, Porto, PORTUGAL, 2011. Method forEevaluation of Concrete Permeability Where: k = air Permeability coefficient (m2);. = air viscosity at room temperature ( );. s = across sectional area of the capillary tube (m2);. l = specimens height (m);. = fluid density used in capillary tube (g/cm3);. S = across sectional area of the specimens (m2);. h0 = initial height (m);. h1 = final height (m);. t = time to go to the net height h0 to h1 (s). The relation ln (h0/h1) = 1 in Equation 1 were employed in order to have laminar flow [Ferreira Jr, 2003]. Heights h0 and h1 when determined by the relation ln h0/ h1 = 1 is based on the same considerations to guarantee that the outflow occurs in laminar regime [YSSORCHE et al.]