Model for Predicting Protective and Decorative. Exterior Walls

Transcription

1 Cntemprary Engineering Sciences, Vl. 8, 2015, n. 2, HIKARI Ltd, Mdel fr Predicting Prtective and Decrative Eterir Walls V. I. Lganina Street Titv, 28, Penza, Russia Cpyright 2014 V. I. Lganina. This is an pen access article distributed under the Creative Cmmns Attributin License, which permits unrestricted use, distributin, and reprductin in any medium, prvided the riginal wrk is prperly cited. Abstract A mdel f service life, taking int accunt the activatin energy f the aging prcess, the intensity f epsure t ultravilet radiatin, temperature and humidity. Is shwn by the eample f the methd f calculating the life f catings accrding t the accelerated tests Keywrds: durability, the paint, the calculatin mdel f aging Intrductin Eaminatin Survey results painted facades f buildings shw that the actual service life des nt always crrespnd t the planned. This leads t additinal csts fr the repair f building facades. The current empirical assessment f service life can nt prduce reliable data n the durability f catings, due t the lack f theretical develpment t assess the service life. There are several appraches t frecasting the durability f catings. In [1,2] it was prpsed t evaluate the durability f catings with regard t the internal stresses. Hwever destructin f cverings is caused nt by ne kind f influence nly vltage, but als humidity bth slar illuminatin and ther factrs. In wrk [3] it is ffered t estimate durability f cverings н by results f the accelerated tests with use f linear dependence н n duratin f the accelerated у tests. Hwever at applicatin f varius paints the linear mdel has a varius kind. It reduces reliability f frecasting. The analysis f the scientific and technical literature testifies, that questins f

2 78 V. I. Lganina frecasting remain actual. In this regard, the creatin f an evidence-based methd fr predicting service life is an imprtant scientific, technical and ecnmic prblem. The aim is t develp a methdlgy fr assessing the life f catings eterir walls. Methdlgy Justificatin f the cmpleity f the mathematical mdel is difficult nature f the mechanism f aging catings. In the peratin f prtective and decrative catings eterir walls, the character f the aging mechanism, ie, at different stages f aging change f peratinal prperties f catings determine different cmpnents f the mechanism f aging. It may be: - Chemical prcesses in catings, ccurring as a cntinuatin f the curing prcess, eternal influences nly change their speed, is the chemical prcesses in catings, including n the surface f pigments and fillers, which are the result f eternal influences the reactants (ygen acids, alkalis, water in the case f the hydrlysis, etc.) and activating factrs (light, temperature) (fr eample - hlrvinilvye plymers); - physicchemical prcesses leading t structural changes (supramlecular structure and phase). Hwever, in mst cases, the destructin caused by the simultaneus ccurrence f catings few prcesses. Cnsider the aging prcess frm the perspective f catings therm- fluctuatin thery f strength plymers [4, 5]. Accrding t the mlecular mdel f fracture atms in the tip f a crack due t thermal fluctuatins frm time t time acquire enugh kinetic energy t rupture r recvery if there was a gap. Under the influence f climatic factrs in the cating f internal stresses, the prbability f breaking the bnds in the structure f the cating increases, and their recvery - is reduced. Accrding t the mlecular mdel f the value f the ptential fracture energy needed t break the bnd, is U U v a whereu - is the ptential barrier tearing dwn -actin lcal stress; v a - the amunt f fluctuatin. The magnitude f the ptential energy needed t restre cmmunicatin is (1) U * U v (2) * whereu - a ptential barrier recmbinatin cnnectin with 0 At sme value f stresses in the cating under the influence f climatic factrs * U v U v, the crack des nt grw, while there is a slight change in the decrative and prtective prperties (incubatin perid). At vltages bserved crack grwth, the speed f the prcess v is determined by the relatin

3 Mdel fr predicting prtective and decrative eterir walls 79 v v 1 v 2 (3) where v1 - the crack grwth rate; v2 -the velcity f the fracture clsure As v1 v2 Since the rate f aging is determined by the rate f crack grwth. The frequency f fluctuatins in time f discnnectin at the crack tip is u u ep[ ( U v ) / kt] (4) Since crack grwth rate is v1 u1, in view f frmula (4) v u ep[ ( U v ) / kt] (5) The transitin frm the active t the incubatin perid is bserved at step. In accrdance with frmula (5) cating lifetime may be defined by the frmula wk w dw v where w w, k -initial and final level f damage accumulatin. The slutin f equatin (6) leads t the frm (6) ep[( U v ) / RT ] (7) A Epressin ( U v ) f the activatin energy is aging. It is an effective value and a cmbinatin f the activatin energies f individual prcesses underlying aging catings. The factr is variable depending n the humidity, the intensity f ultravilet radiatin UV Cnsider the effect f humidity and ultravilet radiatin by a factr. As is knwn W (8) where - cefficient f prprtinality, taking int accunt the effect f humidity n the rate f hydrlysis f the film-frming agent W - Humidity. The rate f hydrlysis is prprtinal t the amunt f adsrbed misture, and can be described by the reactin equatin f the first rder ( 1/ t)ln{ C / C} (9) where C - cncentratin f the substance The rati f the aging time when changing humidity will describe the dependence / cnstk (10) 1 2 {(1/ W1 )ln( C / C1)}/{(1/ W2 )ln( C / C2)} Duratin t achieve the same degree f fracture based n the equatin (10) can be determined by the equatin 1

4 80 V. I. Lganina 1 2k1 (11) As humidity reference value is ffered t use the minimum humidity value achieved in the area f peratin [6, 7]. The Results Table. 1 shws the results f eperimental and calculated data n the effect f humidity n the length f aging catings n eample f silicne paint KO-168. The calculated data shwed gd agreement with the eperimental data. Degree cnsistency f estimated cefficients f pair crrelatin. In the calculatin f the cnfidence prbability f The critical value f pair crrelatin cefficients fr the 95% cnfidence prbability and the number f degrees f freedm n = 5 was = The calculated value f the cefficient f pair crrelatin = was that much mre critical and shws a high cnsistency between the eperimental and calculated data. Table 1 The duratin f aging catings KO-168 with the lss f glss 20% Type f The prsity Humidity,% substrate f the substrate,% Withut UV-irradiatin glass / / / /724 prus cement 20,3 914/ / / /401 Nte. Abve the line shws the eperimental data duratin f the test, belw the line calculated data In [6], the results f studies f kinetics f degradatin f catings under the actin f light radiatin are presented. The duratin f the test t the same degree f damage depends linearly n the inverse radiatin intensities (12) 1J1 2J 2 3J 3 cnst k2 Given equatin (12) the duratin f the aging t a predetermined degree f cating damage depends n the radiatin intensity is determined by the relatin 1 2k2 (13) The duratin f the aging f catings t the desired degree f destructin is determined by the rati ep[ U / RT ] k k (14) 1 2

5 Mdel fr predicting prtective and decrative eterir walls 81 With variable perating cnditins (t), use the equatin Bailey dt / 1 where t - the durability f the cating peratin under these cnditins - Cating durability under all perating cnditins In the transitin frm the integral frm fr a finite increments (15) t / 1 The methdlgy fr calculating the life f catings used additivity principle that allws yu t define cnstant perating cnditins, equivalent t the ttal f their destructive effect t variable cnditins f eplitatin. As cnstant cnditins f eplitatin: temperature 273K; minimal achievable humidity; f intensity ultravilet radiatin in this climatic regin. Equivalent time prpsed t determine the frmula W / W )( J / J ) ep[ U / R(1/ T 1/ T )] (17) ( min тек min тек wheret тек - the current perating temperature Algrithm fr determining the duratin f the aging f catings t the desired degree f destructin is as fllws. 1. Determine fr a given climatic regin, in accrdance with the mathematical mdel (14) during the year, which is equivalent t the ttal destructive effect with respect t the cnstant parameters (temperature, humidity, radiatin intensity ). Yu must first determine the value f the effective activatin energy U. Determine the intensity f climatic tests with the regime and the number f test cycles тек (16) t2 N where N - the number f test cycles; - the intensity f ne cycle f climatic test,day. Determine the lifetime f the frmula (18) (19) Belw is an eample f calculating lifetime plyvinyl-acetate-cement (PAC) and silicne (КО-166) catings. When calculatins were made using the average mnthly value f the intensity f ultravilet radiatin with wavelengths less than 400 nm, relative humidity fr a mderately cld climate. Preliminary studies and calculatins fund that the activatin energy f PAC cating is U = 92,230kDzh / ml, cvering KO kj / ml.

6 82 V. I. Lganina Accelerated testing was perfrmed under the regime: 4 hurs - freezing at -40 C, 2 hurs - thaw in air at a temperature f 40C and a relative humidity f 60%, 2 hurs - misture at a temperature f + 20 C, 16 hurs - ultravilet radiatin at a temperature f + 20 C and a relative humidity 70%. The results f the calculatin are given in Table 2. Table2 Equivalent cating peratin with respect t 0 C in different climatic znes mnth Mscw Yakutsk Vladivstk January 0,61/0,58 0,001368/0, ,34/0,323 February 0,695/0,67 0,0065/0,0056 0,56/0,54 March 5,64/5,54 0,318/0,288 6,74/6,65 April 28,525/19,34 15,86/15,85 28,52/28,92 May 90,32/94,2 39,41/40,2 98,87/75 June 191,32/202,29 169,38/178,32 131,30/137,35 Jul 300,99/ ,05/346,80 278,54/295,85 August 181,00/191,65 149,95/157,95 294,63/315,79 September 51,0/56,5 29,97/30,26 111,92/116,74 Octber 3,05/12,41 1,93/1,88 29/30,42 Nvember 2,44/2,4 0,0327/0,029 2,78/2,78 December 0,664/0,65 0,002/0,0017 0,492/0,47 in ttal 860,35/906,86 716,25/771,6 871,75/1010,84 Nte. Abve the line shws the values fr PAC cating belw the line - cating KO-166. Plyvinyl-acetate-cement cating (PAC) cating When the air temperature -40 C during tests, equivalent time at 0 C is ехр( : ( )) 0, 00013day 24 R When the air temperature f 20C and a relative humidity f 100% is equivalent t the time * ехр( : ( )) 1, 58day R When the air temperature + 20 C. 70% relative humidity and epsure t ultravilet radiatin equivalent time is

7 Mdel fr predicting prtective and decrative eterir walls * * ехр( : ( )) 22, R Therefre, a test cycle is equivalent t days. at 273 K. The number f test cycles at ,16*120=4099,84 day The service life f catings is equivalent t - Mscw 4099,84 4,78year 860,35 -Yakutsk 4099,84 5,72year 716,25 -Vladivstk 4099,84 4,7 year 871,75 Organic silicn cating КО-168 When the air temperature -40 C during tests, equivalent time at 0 C is ехр( : ( )) 0, 00013day 24 R When the air temperature -40 C and a relative humidity f 60% is equivalent t the time * ехр( : ( )) 11, 51day R When the air temperature f 20 C and a relative humidity f 100% is equivalent t the time * ехр( : ( )) 1, 58day R One test cycle is equivalent t days at a temperature f 273 K. The number f test cycles is ,32*200=7465,59day The service life f catings is equivalent t in Mscw 7465,59 8,24year 906,86 - Yakutsk 7465,59 9,65year 771,6 -Vladivstk day

8 84 V. I. Lganina 7465,59 7,38year 1010,84 Results f field tests have cnfirmed that the discrepancy between the predicted and the real life des nt eceed 15% Findings Frmulated the scientific and methdlgical basis f frecasting resistance f prtective and decrative catings eterir walls building. A mdel f aging catings, taking int accunt the type and structure f the cating, the intensity f the impact f climatic factrs. References [1] P. I. Zubv, L. A. Suhareva. Structure and prperties f plymer pkrytiy. Mscw, Chemistry, 1982,256. [2] G. M. Bartenev. Strength and fracture mechanism plimerv. Mscw, Chemistry, 1984,280. [3] M. I. Karjakina Test cver and paints. Mscw, Chemistry, [4] L. P. Orentlikher, V. I. Lganina, S. I. Mishanin. Metdika life predictin catings, Prceedings f the universities. Building. 9 (1994), [5] V. I. Lganina, O. V. Karpva. By assessing the kinetics f aging catings // Prceedings f the universities. Building. 2 (1998). [6] Orentlikher LP, V I. Lganina VI. On the questin f the destructin f cement cncrete catings Husing, 8 (1999). [7] V. I. Lganina. On the questin f predicting the lifetime f prtective and decrative catings cement cncrete Prceedings f the universities. Building, 3 (1996). Received: December 18, 2014; Published: January 29, 2015