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APLIKACE NEDESTRUKTIVNÍ ULTRAZVUKOVÉ STRUKTUROSKOPIE KE STANOVENÍ PEVNOSTI KOMPOZITU S GEOPOLYMERNÍ MATRICÍ APPLICATION OF NONDESTRUCTIVE ULTRASOUND STRUCTUROSCOPY FOR STRENGTH DETERMINATION OF COMPOSITE WITH GEOPOLYMER MATRIX David BÍLEK a, Břetislav SKRBEK b, Tomáš JÍRA c a Technická univerzita v Liberci, Studentská 2, 46117, Liberec 1, Česká republika,
[email protected] b Technická univerzita v Liberci, Studentská 2, 46117, Liberec 1, Česká republika,
[email protected] c Technická univerzita v Liberci, Studentská 2, 46117, Liberec 1, Česká republika,
[email protected]
Abstrakt V posledních letech byly zaznamenány význačné pokroky při vývoji geopolymerních materiálů. Jedná se o amorfní až semikrystalické nanokompozitní látky vznikající geosyntézou. Na základě geopolymerní reakce lze získat materiály, které konkurují např. tradiční keramice, a to bez nároků na vysokoteplotní procesy. Tyto materiály nabízejí široké a různorodé uplatnění. Pro svou extrémní odolnost mohou sloužit jako vynikající izolace a stavební materiál. Do budoucna může být velmi podstatná stabilizace nebezpečných a radioaktivních odpadů pomocí geopolymerních matric nebo schopnost zpracovat jako surovinu pro výrobu geopolymerů odpadní produkty z teplárenských a energetických provozů. Mají řadu překvapivých vlastností, jako jsou nerozpustnost ve vodě, nehoří ani nevytvářejí zplodiny, jsou odolné k teplotám kolem 1000°C, atd. Příspěvek popisuje možnost nedestruktivního stanovení pevnosti v tlaku u válečků z geopolymeru. Jedná se o aplikaci ultrazvukové strukturoskopie, kde se využívá znalost rychlosti šíření ultrazvukových vln v závislosti na struktuře měřeného materiálu. Vzorky použité v experimentu charakterizují kompozitní geopolymerní materiál s různými druhy pojiv. Obecně strukturoskopie využívá vztah mezi fyzikálně měřenou veličinou a mechanickou vlastností materiálu. Výsledná vlastnost se poté získá pomocí experimentálně stanoveného matematického vztahu, modelu. Pomocí ultrazvukové strukturoskopie jsme tedy schopni stanovit s určitou přesností námi požadovanou vlastnost, a to vše nedestruktivní, rychlou cestou. Hlavní cílem experimentů bylo z naměřených hodnot určit matematické modely s co nejvyšším koeficientem korelace, tedy mírou spolehlivosti modelu. Klíčová slova: Geopolymery, strukturoskopie, rychlost ultrazvuku Abstract Considerable advances were noted at development of geopolymer materials in last years. It is concerned with amorphous upto semicrystalline nanocomposite matters generated by geosynthesis. The materials which are able compete with e.g. traditional ceramics can be obtained on basis of geopolymer reaction respectively without requirement of high temeperature processes. These materials offer wide and miscellaneous use. They can serve like excellent insulation and building material due their extreme resistance. The stabilization of dangerous and radioactive wastes using geopolymers matrix or ability for fabrication like a material raw for geopolymer manufacturing from wastes from heat and power stations can be very significant for future. They own many of surprising properties such as insolubility in water, they do not burn and do not form by-products, they are heat resistant upto 1000 °C, etc. 1
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This contribution describes possibility of non-destructive determination of compression strength of cylinders from geopolymer. It is application of ultrasound structuroscopy where is the knowledge of ultrasound waves propagation velocity in dependence on measured material structure used. The samples used in the experiment characterizes composite geopolymer material with various binders. The structuroscopy employs the relation between measured quantity and mechanical property of material generally. The resulting property is obtained using experimentally determined mathematical relation, model after it. We are able to determine by us required property with definite accuracy using ultrasound stucturoscopy namely in non-destructive, rapid way. The main aim of experiments was determination of mathematical models with highest possible correlation coefficient i.e. measure of model reliability from asmeasured values. Key words: Geopolymers, strukcturoscopy, velocity of ultrasound 1.
ÚVOD
The rapidly developed scale of modern materials is leant mainly on destructive diagnostics of structure at research and experimental production. But we are able relatively easily and mainly quickly to determine mechanical properties of investigated materials using non-destructive structuroscopy. It is enough for it to know the experimentally obtained mathematical relation between ultrasound waves velocity and structure of given material. In order to reach this relation it is necessary to create the set of samples for each type of materials, using them is necessary experimentally find the dependence of structure and acoustic properties of materials. Rising technologies and modern construction nano-materials in step of research and development go without non-destructive testing and diagnostics. But experiences from research history teach that with NDT is created the competitiveness of their production. The created feedback in manufacturing ensure perfect outlet quality. 1.1
Geopolymers
The question what is it the geopolymer is not easy to answer. As for the most brief description, the word „Geopolymer“ should mean verbally artificial stone, or artificially created stone. The application of these materials has appeared before more than 4500 years already at pyramid builders after one of hypothesis. The development of geopolymers notes considerable progress presently. This material offers due its specific properties wide and miscellaneous use. The considerable compression strength, thermal resistance, but also chemical stability belong among such properties. If we want create geoploymer mixtures, we need raw materials, which contain compounds of SiO2 and Al2O3. It means that even alkaline activations of waste products (power station ash, shale and various slags) are sufficient for geopolymer manufacturing. Geopolymer manufacturing owns its rules and principles, that must be kept similarly like at concrete mixture manufacturing. We can put a question today: Will the material revolution come? Geopolymers could be the acceptable material, replacing classical concretes not only in common building, but also in sophisticated applications as are bridgeworks.
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2.
ULTRASOUND STRUCTUROSCOPY
Basic principle of non-destructive ultrasound structuroscopy is experimental determination of mathematical relation (model), that characterizes mutual connection between ultrasound waves velocity (damping) and structure of investigated material (mechanical property). It si concerned with theory of interaction between ultrasound waves and boundary in material, where is possible to find mutual correlation between ultrasound waves velocity and structure, rather mechanical property of material. The ultrasound waves velocity depends on damping size in transradiated material. It means that its value shall differ in case of steels, cast irons, polymers or composites.
Thus the ultrasound waves velocity sinks with increasing damping of matrix mass and especially with amount and size of internal discontinuities. The discontinuities are reinforcements, layers, inclusions with considerably different wave resistance Z against matrix. [MPa/s]
(1)
The fraction R of reflected pressure of acoustic wave back from boudary increasis with increasing difference of acoustic resistances Zm a Zg. Zm = 5,92·7,8 = 46,2 MPa/s is valid for steel matrix. Zg = 2·2 = 4 MPa/s is valid approximately for carbon in the shape of graphite. R = (Zg - Zm)/(Zg + Zm) = 0,805 after inserting. One boundary matrix – graphite so reflects R = 80,5% of pressure of acoustic wave. Direct propagation of acoustic wave through composite is after several reflections from formations of reinforcement consumed and dispersed. Path size of acoustic wave in matrix depends on labyrinth of path through matrix. The value of acoustic path Lu increases in comparison with direct path (thickness of transradiated wall) L with decreasing thickness of formations. Thus ultrasound velocity cL sinks.
5920
[m/s]
(2)
cL0... ultrasound velocity in steel (etalon for setting of ultrasound instrument). Boundary character expresses oneself on phase of reflected wave. The boundary with lesser wave impedancy reflects wave in opposite phase than boundary with higher impedancy. This effect if often used in fibrous or layered systems of materials. The highest stair of structure diagnostics is created by spectral analysis of acoustic response (echos, noise). The damping of acoustic oscillations a increases considerably, if wavelength l approaches to size of reinforcement d. [1.] ∝
∝
[dB/mm]
(3)
Value a = 0,05 for steel enables to transradiate even meter thicknesses of walls. Non-metallic reinforcement in metallic matrix increases the damping considerably. It achieves a values of higher order, it limits acoustic diagnostics heavily. The ultrasound measurements of austenite steels and graphite cast irons are complicated by austenite gran boundaries and cast iron graphite. The low frequency probes upto 2MHz are inecessary for measuring of wall thickness over 30 mm. If the reinforcement by its demensions d<
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steel owns length of longitudinal wave 1,2 mm, polymers, water cca 0,3 mm for most common ultrasound frequency 5 MHz. E value depends directly on size of sound velocity cL.
,
[m/s]
(4)
[MPa]
(5)
The simplified expression is used in practice
…where K is measured on slender cylindrical sample. Ultrasound structure diagnostics requires parallel planes of walls in site of checking. The value of measured Lu is increased by surface roughness (ammount of binding medium (cL 1500m/s in the interspace under probe) and „V“ effect of ultrasound probe on thin walls, so that checking of walls upto L 10mm is inaccurate. [2.] 3.
EXPERIMENTAL
Materials on basis of geopolymer nano-composites in shape of cylinders with diameter cca 10 mm were used for experiments. Thus it was boundary geopolymer matrix – reinforcement. The reinforcement was the ~ R10 L a Lu
filler (shale, ash and stone).
¨ Obr. 1. Použité vzorky Fig. 1. Used samples The acoustic path Lu and actual path L of all samples (10 pieces for each type of reinforcement, total 40 pieces) were measured using ultrasound defectoscope DIO 562 and ultrasound probe 1 MHz. To obtain models characterizing sample strength, the regression analysis of as-measured data (see Table 1.) was necessary. The tables describe as-measured values L, Lu, ultrasound waves popagation velocity cL and average compression strengths R divide to two tables after type of filler. The raw without filler means only polymer matrix. Figure 2 characterizes the effect of additives on compression strength R and ultrasound waves velocity cL in as-investigated material. The linear dependence between strength and type of additive is obvious, where the largest effect on strength has just ash additive. The dependence of ultrasound velocity values on type of additives is similar, with following difference that maximum values cL are obtained for samples with 50% shale additive, thus more than at samples without additives. It means that shale as a additive do not resist against ultrasound waves propagation and on the contrary its damping is so far smaller than in case of samples without additive. But the shale has negative effect on compression strength, as for mechanical properties. 4
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Tab. 1. Naměřené hodnoty vzorků podle druhu přísad Table 1. As-measured values of samples by kind of additives Average Sample cL Type of L Lu strength no. [m/s] additive R [MPa] 1 24,1 33,97 4214,1 2 24,2 33,97 4231,6 3 24,9 35,08 4216,3 4 24,5 34,15 4261,5 5 24,5 34,53 4214,6 110 without 6 24,5 34,15 4261,5 7 23,9 33,22 4273,5 8 24,8 34,71 4244,1 9 25 35,08 4233,2 10 23,7 33,04 4260,8 Average Sample cL Type of L Lu strength no. [m/s] additive R [MPa] 1 26,5 41,59 3784,8 2 27,2 41,89 3857 3 26,7 41,02 3866,4 4 26,5 39,54 3981 5 26,8 40,47 3933,6 Stone 58,77 20% 6 26,6 40,28 3922,6 7 26,6 41,59 3799,1 8 26,4 40,46 3875,8 9 26,7 40,09 3956,1 10 26,7 40,65 3901,6
Compression strength [MPa]
Effect of additive on cL Value cL [m/s]
5000 4500 4000 3500
L
Lu
cL [m/s]
Average Strength R [MPa]
Type of additive
28,1 26,4 27,1 27,1 27,3 26,5 26,4 26,9 26,8 27
38,11 34,15 36,57 36,57 36,57 36,01 35,89 36,75 34,34 35,27
4379,8 4592 4401,8 4401,8 4434,3 4371,3 4369,4 4347,9 4635,8 4547,2
73,04
Shale 50%
L
Lu
cL [m/s]
Average strength R [MPa]
Type of additive
27,6 27,9 27,8 28 27,8 26,3 27,3 27,2 26,9 27,5
51,41 51,87 50,49 51,97 50,86 48,81 50,12 50,89 49,38 50,12
3189 3195 3270,6 3200,3 3246,8 3200,6 3235,5 3174,9 3235,8 3259,2
42,63
Ash 20%
Effect of additives on strength 120 100 80 60
3000
40 1
2 3 4 Type of additive
1
2
3
4
Type of additive
Obr. 2. Vliv přísad na rychlost ultrazvuku cL a pevnost v tlaku R Fig. 2. Effect of additives on ultrasound velocity and compression strength R 4.
CONCLUSION
The aim of experiments was to determine mathematical models characterizing dependence between compression strength and ultrasound waves propagartion velocity in the investigated material. Figure 3. lillustrates this dependence and in Table 2 are final models for non-destructive determined compression strength. It is obvious growing exponential dependence between as-measured values of ultrasound waves 5
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velocity and compression strength of samples. Thus the strength of tested material increases withincreasing value of ultrasound velocity (less structure discontinuities and smaller influencing of structure by additive).
Withnout data of shale addition
120 100
y = 6,1485e0,0006x R² = 0,6688
80 60 40 3200
3650
4100
4550
Compression strength [MPa]
Compression strength [MPa]
With shale addition
Velocity of ultrasound [m/s]
120 100
y = 2,413e0,0009x R² = 0,876
80 60 40 3200 3550 3900 4250 Velocity of ultrasound [m/s]
Obr. 3. Závislost mezi pevností v tlaku a ultrazvukovou rychlostí Fig. 3. Relation between compression strength and ultrasound velocity Because the model, which consider even as measured data of samples with shale addition, gived worse reliability (67%), the regression without data characterizing samples with shale addition (reliability 88%) was performed. It is necessary to perform experiment with greater scale of sample properties and more detalied analysis of samples containing shale addition in order to enhance reliability of models. The aim of experiment was the effort to apply non-destruktive ultrasound structuroscopy on material othe than graphite cast iron, where the similar experiments were performed formerly and were ver successful (reliability of models about 98%). This method makes easy and accelerates together verification of material quality from point of view its structure, when the destructive measuring of mechanical properties becomes needless. Tab. 2. Konečné modely pevnosti v tlaku Table 2. Final models of compressive strength Modely 3,591(L/Lu) R = 6,148e 5,172(L/Lu) R = 2,419e
Míra spolehlivosti K v % 66,8 87,6
This contribution was made with submissiom of VZ MSM 4674788501. REFERENCES [1.]
OBRAZ, J. Zkoušení materiálu ultrazvukem. Praha: SNTL, 1976.
[2.]
SKRBEK, B. Nedestruktivní materiálová diagnostika litinových odlitků. Disertační práce, VŠST Liberec, 1988.
[3.]
BÍLEK, D., and SKRBEK, B. Parameterization of apparatus TELIT. In Mikroskopie a nedestruktivní zkoušení materiálů: 1. mezinárodní konference. Ústí nad Labem: Univerzita J.E.Purkyně, 2010, [CD ROM]. ISBN 978-80-7414-280-2.
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