REUSE OF TREATED ASBESTOS CONTAINING WASTE AS ARTIFICIAL POZZOLAN AND COMPARISON WITH COMMERCIAL MICROSILICA

Transcription

1 REUSE OF TREATED ASBESTOS CONTAINING WASTE AS ARTIFICIAL POZZOLAN AND COMPARISON WITH COMMERCIAL MICROSILICA A. KOUKOUTSAKI*, A. VALOUMA* AND E. GIDARAKOS* * School of Environmental Engineering, Technical University of Crete, Akrotiri University Campus, Chania 731 Crete, Greece SUMMARY: Two of the most important areas of study in modern society are the construction sector and the protection of the environment. Two interrelated sectors where one serves the needs of the other with many different application fields. In this research, the relationship between the management of asbestos cement waste and its use by the construction sector will be studied. In particular, asbestos cement, which constitutes a danger to human health and is one of the most common applications of asbestos-containing materials, has been processed for detoxification and its use as a reinforcing material in the preparation of mortar specimens. Four different forms of treated asbestos cement were studied, as regards their pozzolanic properties and reuse possibility. The products obtained after processes are mainly amorphous silica mineral and their reuse in mortars preparation is proposed. In this study investigated the relationship between chemical determination of pozzolanic activity, Chapelle test, and the impact of these materials in mechanical properties of the concrete. The results of studied specimens mechanical properties were compared with a reference standard test specimen without addition of treated asbestos cement and with a specimen to which a commercial reinforcing material of similar properties and characteristics was added. Satisfactory results yielded with regard to the use of the test materials as additional mortar reinforcers. These treated asbestos cement materials have provided mechanical properties similar to or even better than existing commercial material in some specific proportions 1. INTRODUCTION In the field of Environmental Engineering, recycling and re-use of materials hold a major role. Recycling is an action aimed primarily the protection of the environment, human health and the conservation of natural resources. In order to render recycling viable, information, prevention and proper waste management is required. Waste management varies depending on the category. Each category of waste is integrated into alternative management and is followed by a statutory legal framework. Concrete remains one of the predominant construction materials consisting of sand broken stone or other inert materials mixed in mortar or cement matrix. Concrete often is not only a mix of cement water and inert composites. Nowadays, more and more frequently components with specific characteristics are added in the initial mixture, in order to react with cement and offer advantageous Proceedings CRETE 218, Sixth International Conference on Industrial & Hazardous Waste Management Chania Crete Greece; 4 7 September 218 ISSN:

2 properties in comparison to ordinary Portland cement based concrete. As a result, these reinforced concretes usually produce more complex mechanisms in the phase of hydration, reactions take place between additives and cement paste while in parallel amorphous materials tend to interact with organic parts of cement matrix. The reinforcement of concrete using particles at micro and nanoscale gains the scientific interest and industrial s sector attention. Silica micro and nanoparticles are preferred due to their excess of reactive amorphous SiO2 and high specific surface area, characteristics that aim the pozzolanic reaction to be conducted (Bahadori & Hosseini, 212). Silica particles are capable to react with free calcium hydroxide (CaOH2) of cement paste. This reaction leads to the formation of calcium-silicate-hydrate (C-S-H) gel formation. As a result, free calcium hydroxide in the matrix reduces while in parallel the strength of the hardened mortar increases. The science of concrete is expected to be centerpiece of research next years, such as new types of concrete are developed under environmental perspective and due to emerging socio-economic needs. Recycling of secondary raw materials in concrete industry steadily occupies the attention of researchers (Gjorv & Sakai, 214, Khalaf, & DeVenny, 24). High environmental impact of cement production associated with increasingly demand for concrete of infrastructure sector, leads to the development of alternative solutions through the use of recycled materials. Recycling of both hazardous and non-hazardous raw materials induce a positive sign comparing with the widely applied disposal of construction waste to landfills. An important hazardous waste in European countries is Asbestos Containing Waste. Asbestos was extensively used as raw material in construction sector, mainly in 2 th century. Since the early 9 s, asbestos use was banned in several countries due to its harmful consequences in human health, provoking asbestos signature diseases (lung cancer, asbestosis, mesothelioma). Besides asbestos use is banned, it is still commonly found in the environment and buildings. ACW are considered to be an emerging problem, such as renovations of buildings are going to produce huge amounts of ACW. Even if the disposal of ACW in hazardous waste landfill site is the most common method, it is not a permanent solution, such as fibers dispersion is not able to be prevented (Gualtieri et al., 211). This paper describes the possibility of recycling modified ACM to amorphous silica as artificial pozzolan. The products under study are result of experimental research on ACW detoxification. These products, derived from chemical treatment of ACW, are characterized of high amorphous silica content (7-9 %wt) and CaO in crystalline phase of calcium oxalate monohydrate, whewellite (8-2 %wt). It was firstly investigated their pozzolanic properties via Chapelle method (NF P ). This method was chosen in order to determine the reactivity of these artificial pozzolans before their embodiment to mortars, measuring the lime consumption of modified materials according the standard method. Afterwards, it was added the artificial pozzolans in cement matrixes, in different concentrations. It was also studied the compressive strength of specimens and the effect of concentrations on water to binder ratio. All the above mentioned methods were conducted on the proposed materials and commercial microsilica (silica fume) for comparison purposes. 2. MATERIALS AND METHODS 2.1. Materials Two different materials of siliceous composition where used. One products originated from ACW after treatment and commercial silica fume SF 92-D (Topken). Silica fume was chosen because its chemical composition and particle distribution is similar with the materials under study (Table 1, Figure 1). In order to conduct the experimental investigation Portland cement CEMII/A-LL 42.5 Ν (FINOMIX), standard sand (S.N.L.) according to EN 196-1, sugar and Ca(OH)2 (Merck) were supplied. CRETE Sixth International Conference on Industrial & Hazardous Waste Management 2

3 Table 1. Chemical composition of proposed materials, silica fume and portland cement A-LL 2.2. Methods MW AP STF SF 92-D PC_LL SiO CaO MgO Na2O K2O TiO MnO Fe2O Al2O SO LOI Σύνολο Chapelle Test The test conducted according to NF P that indicates pozzolanic properties of materials under study as measuring the reduction of Ca(OH)2 by combination with possible pozzolans. In this present study case, a mixture of 3g of CaO and 2g of pozzolan was placed in a Erlenmeyer with 25 ml of distilled water, and set in a silica oil bath at 9 ºC during 16 h. A control mixture is made under the same condition but only with CaO. A solution of 6g of sugar and water up to 25 ml was added in order to dissolve the free Ca(OH)2. The solution was then filtered and titrated with,1m HCl, being the amount of calcium consumed determined by equation 1: mg CaO = 2 x ((v2-v1)/v2) x 74/56 x 1 (eq. 1). v2 is the titration volume of the control mixture (CaO) and v1 is the titration volume of the pozzolanic mixture (CaO + pozzolan). According to the method, if CaO consumption is higher than 66 mg, the material is considered a pozzolan. (Quarcioni et al., 215) Particle size (μm) MW AP STF SF Figure 1. Particle size distribution of materials under study Ultrasonic pulse velocity Of the non-destructive techniques, the ultrasonic pulse velocity technique offers the lowest cost of CRETE Sixth International Conference on Industrial & Hazardous Waste Management 3

4 use and is convenient as well as rapid to employ. The principle of assessing quality of specimen is that comparatively higher velocities are obtained when the quality of mortar in terms of density, homogeneity and uniformity is good. In case of low quality, lower velocities are obtained (Table 2). Then, the velocity is calculated according: V= L/T, where V = pulse velocity (m/s), L = length (m), and T =effective time (s), The zero-time correction is equal to the travel time between the transmitting and receiving transducers when they are pressed firmly together. The UPV results can be used: To check the uniformity of mortar To detect cracking and voids in mortar To control the quality of mortar and mortar products, by comparing results to a similar made mortar Table 2. Quality of specimens (BS, 1881, 1983) as a function of UPV UPV (m/s) Quality 1 Above 45 Excellent Good Medium 4 Below 35 Doubtful 3. RESULTS 3.1. Chapelle Test A relatively wide result variation was observed in studied materials. The composition of the samples present similarities regarding their amorphous phase and particle size distribution. Nevertheless, each of the samples presents different results on CaO consumption during Chapelle test. We can observe that commercial product SF consume the highest quantity of CaO. STF sample, besides contains lower concentration of amorphous silica than GEL, seems to react better as pozzolan according to that chemical method. Figure 2 illustrates the calcium consumption of the proposed as pozzolanic materials that has been analyzed in this experimental research. All of them are able to consume more than 66 mg of Cao, which is the lowest limit to be considered pozzolans, according to the method. Only SF and GEL materials were studied as additives in mortar specimens due to their similarity concerning particle size distribution (Figure 1) Compressive strength According to the experimental results of cement and reinforced cement specimens in Figure 3 the compressive strength is increasing as lower is the additive concentration. The strength of the mixture containing one of the proposed artificial pozzolan is higher in comparison with the one with SF in same concentration. Mixtures containing high amounts of pozollans show lower strengths. According Table 2 the mixtures with high percentage of pozzolan demand more water in order to obtain the desirable fluidity and workability. This water, even if it is necessary to obtain the preferred mixture, it also produce voids in the cement paste matrix during the curing, resulting lower quality mortar. CRETE Sixth International Conference on Industrial & Hazardous Waste Management 4

5 mg CaO Chapelle AP SF MW STF Figure 2. mgcao consumption according Chapelle test High concentration of SF and/or AP in cement matrix agglomerate and form low strength voids, which connect with the existing voids in addition to reducing the durability of specimens. Concequently, these negative effects prevail over the positive effects of pozzalonic behavior micro scale particles of amorphous silica, and damage the specimens structure (Redon & Chermant, 21). Particle size distribution is also significant to the pozzolanic reaction. Smaller particles facilitate the reaction between silica particles and Ca(OH)2 crystals. These microscale particles contribute significally to the development of the desired C-S-H gel according the equation: Si OH + Ca 2+ +2OH - C S H (eq. 3) (Hosseinpourpia et al., 212) Compressive strength 28d Gel SF Reference Gel SF Reference Figure 3. Compressive strength of cement speciments reinforced with SF and Gel (2.5-1 %wt) UPV and strength of mortars with low w/c are higher than those with high w/c as illustrated in Table 2 and Figures 3 and 4 mainly because of the denser structure of mortars with lower w/c. CRETE Sixth International Conference on Industrial & Hazardous Waste Management 5

6 Compressive strength (MPa) Table 3. Water to binder ratio of selective mixtures Pozzolan Additive W/C Gel SF Reference , 4, 3, 2, 1, Ultrasonic Pulse Velocity Reference 2.5% Gel 5% GEL 1% GEL 2.5% SF 5% SF 1% SF Figure 4. UPV of mortar specimens through age According to Figure 5, there is a high correlation (R 2 =.97) between the ultrasound pulse velocity and the compressive strength. The quality of the mortar, considered of good quality if V> 35 m/s. This present correlation with the results of compressive strength of specimens under study. For the purpose of calculating this correlation, only the results of UPV values were greater than 4 m/s were taken under consideration. These results corresponded to the compositions with 2.5 and 5% of the added materials, respectively. Comparison of Av. Velocity and compressive strength y =.114x R² = Velocity (m/s) Figure 5. Comparison of UPV and compressive strength of specimens CRETE Sixth International Conference on Industrial & Hazardous Waste Management 6

7 In summary, it is concluded that the quality of the mortar in the first days of curing for compositions with high water / cement ratios is quite low. Over the time and up to the 28th day, there is a significant improvement. However, early strengths (up to 7 days of curing) are expected to be particularly low, as according to the literature (Lawson et al., 211) equate to about 3% of the corresponding strengths at 28 days. 4. CONCLUSIONS The material that offer the highest compressive strength, as pozzolanic additive to cement matrix, is the proposed modified pozzolan AP, and specifically as cement replacement in percentage 2.5%, exhibiting mechanical properties better than those of the same cement replacement with the commercial SF. Furthermore, AP as additive, contains high concentration of amorphous silica and a small amount of CaO. The addition of these phases in mortar mixture also facilitates the pozzolanic reaction and the formation of strong C-S-H bonds. Regarding the speed of ultrasonic pulse measurement, there is a variation in the Ultrasonic Pulse Velocity over the days of curing. It is concluded that at low concentrations of admixtures, the quality of the mortar is better than the first stages of maturation. High water concentration, key factor in cement hydration, block the hydration reaction, increases porosity and, as a result, degrades the quality of the mortar. It is also concluded that even if SF consumes higher amount of CaO, according to Chapelle test, AP present better pozzolanic behavior, probably due to smaller particles size and small quantities of free Ca(OH)2 in the sample, that facilitate pozzolanic reactions. REFERENCES Bahadori, H., Civil Engineering and Management, 18(3), CEN, EN 196-5: 25 Methods of testing cement - Part 5: Pozzolanicity test for pozzolanic cement, Brussels, 25. Chen, R. S., & Ye, Q. (22). Research on the comparison of properties of hardend cement paste between Nano-Sio2 and silica fume added concrete. Hosseinpourpia, R., Varshoee, A., Soltani, M., Hosseini, P., & Tabari, H. Z. (212). Production of waste bio-fiber cement-based composites reinforced with nano-sio2 particles as a substitute for asbestos cement composites. Construction and Building Materials, 31, Gjorv, O., & Sakai, K. (214). Concrete technology for a sustainable development in the 21st century. CRC Press. Gualtieri, A. F., Giacobbe, C., Sardisco, L., Saraceno, M., Gualtieri, M. L., Lusvardi, G., & Zanatto, I. (211). Recycling of the product of thermal inertization of cement asbestos for various industrial applications. Waste management, 31(1), Khalaf, F. M., & DeVenny, A. S. (24). Recycling of demolished masonry rubble as coarse aggregate in concrete. Journal of materials in civil engineering, 16(4), Lawson, I., Danso, K. A., Odoi, H. C., Adjei, C. A., Quashie, F. K., Mumuni, I. I., & Ibrahim, I. S. (211). Non-destructive evaluation of concrete using ultrasonic pulse velocity. Research Journal of Applied Sciences, Engineering and Technology, 3(6), Pontes, J., Santos Silva, A., & Faria, P. (213). Evaluation of pozzolanic reactivity of artificial pozzolans. In Materials Science Forum (Vol. 73, pp ). Trans Tech Publications. Quarcioni, V. A., Chotoli, F. F., Coelho, A. C. V., & Cincotto, M. A. (215). Indirect and direct Chapelle's methods for the determination of lime consumption in pozzolanic materials. Revista CRETE Sixth International Conference on Industrial & Hazardous Waste Management 7

8 IBRACON de Estruturas e Materiais, 8(1), 1-7. Redon, C., & Chermant, J. L. (21). Compactness of the cement microstructure versus crack bridging in mortars reinforced with amorphous cast iron fibers and silica fumes. Applied Composite Materials, 8(3), CRETE Sixth International Conference on Industrial & Hazardous Waste Management 8