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MICROSTRUCTURE ANALYSIS OF THE STRUCTURE OF MATERIALS USED FOR THE MIXTURE OF EXPANDED – CLAY LIGHTWEIGHT CONCRETE

WITH ADDITIVES OF RAW MATERIAL

Romualdas Mačiulaitis, Marija Vaičienė, Ramunė Žurauskienė

Vilnius Gediminas Technical University, Sauletekio ave. 11, LT-10223 Vilnius, Lithuania. E-mail: romualdas.maciulaitis@vgtu.lt, marija.vaiciene@vgtu.lt, ramune.zurauskiene@vgtu.lt

Abstract. In order to utilise various waste materials as additives in the production of lightweight concretes effi-ciently, it is necessary to carry out a detailed analysis, to determine their mineralogical, chemical, granulometric composition. The purpose of this research is to analyse the properties of raw materials, used in the production of ex-panded-clay lightweight concrete with the catalyst waste, and estimate their influence on the properties of the mixture of lightweight concrete. Microstructure of the analysed Portland cement and catalyst utilised in the reactor of catalytic cracking, X-ray structural analysis of waste material is provided in the research. Additionally, the analysis of the crush resistance of coarse aggregate (expanded-clay) carried out, is described in the research. The granulometric composition of the sand was determined, as well as the particles' size of the catalyst and cement was analysed. The hardened expanded clay – lightweight concrete was analysed during the research. Microstructure analysis of the ex-panded-clay lightweight concrete was carried out.

Keywords: filler aggregate, expanded-clay aggregate, waste catalyst, lightweight concrete, microstructure.

1. Introduction

In recent years it is important for the manufacturers to use cheap raw materials for the production of construc-tion materials. In order to compete in a market, the manu-facturers are putting a lot of efforts to lower the produc-tion costs, because by lowering the costs the manufacturers can offer their production in the prices, lower than ones of competitors. During the manufactur-ing of products from the secondary raw materials the several problems increasing product's costs are faced. During the manufacturing of products from the secondary raw materials it is necessary to follow the same require-ments applied for the products from the initial raw mate-rials. Moreover, special requirements related to the usage of secondary raw materials must be complied with. Addi-tional problem lies in the negative image of these prod-ucts, and this image does not contribute to the increase of demand and selling of the production (Uselytė et al. 2007). However, during the implementation of waste reprocessing and utilisation programmes in future, part of the natural materials will have to be replaces by raw ma-terials. Due to this waste materials must be used instead of the natural resources where it is possible.

Already a decade scientists from various countries are analysing the secondary usage of catalyst waste. Cata-

lyst waste is created in the oil refineries, in the equipment for catalytic cracking. Here the coarse-grained and fine-grained particles of the utilised catalyst are created. The coarse-grained particles are created during the filter cleaning. They consist of more than 55 % of SiO2 and 40 % of Al2O3.

During the scientific investigations it was found, that when fine-grained catalyst waste is used (Su et al. 2000), it is possible to replace 15–20 % of the grout of binding material in the mixtures or 10 % of fine-grained aggre-gates without worsening grout's qualitative properties.

Due to the special chemical composition and appro-priate characteristics, this catalyst waste can be used for the production of fire resistant (Stonys et al. 2008) and ceramic products (Mačiulaitis et al. 2007), and can be used as an aggregate in the production of asphalt concrete or as a pozzolanic component for Portland cement (Fu-rimsky 1996) as well.

Recently, chemical and active mineral additives are introduced widely in the concrete production technology. These additives influence largely water’s binding forms of and its amount in the concrete mixture or grout, rheological properties of the mixtures and hydration of the cement. Active dispersive additives (mostly industrial waste materials, having large amount of amorphous SiO2) are used as partial replacement of cement in the concrete

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mixtures. Due to high excess of dispersiveness and sur-face energy, these additives influence the interaction between water and solid phases in the concrete mixture. By increasing the surface area of solid phase in the mix-ture, active dispersive additives increase the amount of water in the cement paste of normal consistence (Sas-nauskas et al. 2001).

Fine-grained catalyst waste can be assigned to the group of filler aggregates, and, considering its influence during the cement hydration process, to active filler ag-gregates. In reference (LST EN 1577 1999) it is stated that active filler aggregates can be produced from the natural rocks, industrial waste materials. The amount of active SiO2 in these filler aggregates should not exceed 50 %, and should not be less than 5 % (of the mass).

During our previous research (Mačiulaitis et al. 2009) it was found, that when the catalyst waste (15 % comparing to the cement mass) from the reactor of cata-lytic cracking is used for the lightweight concrete, the density of the analysed expanded-clay lightweight con-crete and compressive strength (even for the larger wa-ter/cement ratio) increase, more heat is dissipated during the hydration of cement and this exothermic effect occurs several hours earlier.

During the analysis of the expanded-clay lightweight concrete, where the fractions of coarse aggregates were 5, 15 and 25 mm, scientists (Tommy et al. 2007) have esti-mated that the highest compressive strength was reached after 28 days of hardening of 15 mm fraction expanded-clay. These scientists state that the strength of the con-crete with the light-weight aggregates depends on the strength of the utilised light-weight aggregates and on the strength of hardened cement paste.

The main issue of this research is the utilisation of technogenic raw materials of oil industry for the produc-tion of high quality products of lightweight concrete. The main task of the research is to analyse the fine-grained catalyst waste and estimate its possible influence on the properties of the mixture of lightweight concrete. The analysis of the research shows the possibilities of the production of lightweight concrete by utilising the secon-dary resources. To implement this task the properties of raw materials were analysed, the appropriate content of formation mixture was selected, the structure of hardened expanded-clay lightweight concrete was analysed.

2. Experimental methodology and raw materials

2.1 Experimental methodology

The microstructure of Portland cement, waste cata-lyst, expanded-clay and lightweight concrete particles was observed by a SEM (EVO LS 25, Zeiss Germany).

The chemical composition of the catalyst were esti-mated by using the analyser OXFORD Instruments INCA Penta FET×3.

The X-ray analysis was carried out by X-ray diffrac-tometer DRON-2 with a cooper anticathode and nickel filter, the voltage of anode 30 kV, current of anode 8 mA, slits of the goniometer – 0.5; 1.0; 0.5 mm, the speed of recording of X-ray diffraction patterns – 600 mm/min. the

phase composition was defined using the ASTM card index of data.

The crush resistance of the grains of expanded-clay in dry status is estimated according to LST EN 13055-1 „Lightweight aggregates – Part 1: Lightweight aggregates for concrete, mortar and grout“.

The granulometric composition of the fine-grained aggregates is estimated according to LST EN 933-1 „Tests for geometrical properties of aggregates – Part 1: Determination of particle size distribution – Sieving method”.

The size and granulometric composition of the cata-lyst and particles of the cement is analysed with the ana-lyser CILAS 1090 DRY.

The composition of the mixture of expanded-clay lightweight concrete is calculated by implementing the methodology described in (Skramtaev et al. 1966). Sam-ples – cubes (with 10 cm side length), were hardened in accordance with LST EN 12390-2 2003.

During the analysis of the expanded-clay lightweight concrete with the additive of catalyst waste, the formation mixture with the following composition for 1 m3 was prepared: 292.6 kg of Portland cement, 822.8 kg of sand, 396.5 kg of sand of expanded-clay with the fraction of 0–4 mm, 215.8 l of water and 30 % of used catalyst was poured into the mixture (comparing to the amount of the binding materials), i.e. 125.4 kg. During the analysis of the expanded-clay lightweight concrete with no additive of waste materials, the formation mixture with the follow-ing composition for 1 m3 was prepared: 418 kg of Port-land cement, 822.8 kg of sand, 396.5 kg of sand of ex-panded-clay with the fraction of 0–4 mm, and 215.8 l of water.

2.2 Row materials properties

Cement: Portland-composite cement CEM II/A-L 42.5N (A), from company "Akmenės cementas" AB, complying with the requirements of the standard LST EN 197-1 "Cement – Part 1: Composition, specifications and conformity criteria for common cements". The chemical composition of the Portland cement is provided in Table 1, and mineralogical composition is provided in Table 2. Table 1. Chemical composition of Portland cement

Chemical composition, % SiO2 CaO Al2O3 Fe2O3 MgO SO3 CaO1 Others 20.61 63.42 5.45 3.36 3.84 0.80 0.73 0.341

Table 2. Mineral composition of Portland cement

Mineral composition

C3S C2S C3A C4AF

In % 57.26 15.41 8.68 10.15

Fine aggregate: natural sand with the particles’ size

of 0–4 mm. The granulometric composition of the sand is provided in Table 3. Table 3 shows that the particles with the size from 1 to 0.5 mm compose the major part of the sand, the amount of these particles is approximately 47 %.

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Table 3. Sand's granulometric composition

Size of sieve mesh, mm Partial residue, % form 4 to 2 30.197 from 1 to 0.5 46.73 from 0.25 to 0.125 20.155 ‹ 0.063 1.034

Coarse light-weight aggregate: expanded-clay sand

with 2–4 mm size particles. Characteristics of the coarse aggregate are provided in Table 4. Table 4. Characteristics of the expanded-clay sand

Properties Fraction of ex-

panded-clay

Bulk den-sity

kg/m3

Density of

parti-cles

kg/m3

Hol-low-ness %

Wet-ness %

Im-pregna-tion %

2–4 mm 473 1020 53.63 13.90 33.55

The crush resistance of 2–20 mm fraction grains of the expanded-clay was estimated. The results of the analysis of crush resistance of dry expanded-clay are provided in Table 5. Table 5. Crush resistance of expanded-clay

Crush resistance, MPa Fraction of the expanded-clay, mm

Dry 2–4 3.25

4–10 2.64 10–20 1.39

Filler aggregate: fine-grained catalyst waste from the reactor of catalytic cracking. These particles are pro-duced by using filters. The chemical composition of this catalyst waste is as follows: SiO2 – 55.15 %, Al2O3 – 40.94 %, Fe2O3 – 0.90 %, TiO2 – 1.48 %, P2O5 – 0.11 %, La2O3 – 1.41 %.

Fig 1 shows the X-ray diffraction diagram of cata-lyst waste, indicating that this catalyst is a crystalline material with some amorphous phase in the structure. The crystallized phase identified is mainly faujasite (Na2, Ca, Mg)3.5Al7Si17O48·32H2O.

Results of the analysis of elements' composition in the catalyst waste showed that the following materials exist: Fe – 0.14 %, S – 0.10 %, C – 24.31 %, La – 0.22 %, Ti – 0.10 %, Cu – 0.06 %, O2 – 70.06 %.

0

200

400

600

800

1000

1200

1400

1600

4 8 11 15 18 22 25 29 32 36 39 43 46 50 53 57 61 64

2 Theta: degrees

Inte

nsi

ty (

a. u

.)

+

+

++

++

++

+++

+

+

+

+ Faujasite

Fig 1. X-ray diagram of catalyst

3. Experimental results and discussions

3.1. Microstructure and dispersivity analysis of the materials

The structure of Portland cement used in the re-search is showed in Fig 2. In the photo it can be noticed that the shape of the powder of Portland cement is irregu-lar, and size varies in a wide range. Such properties are typical for Portland cement where the major part is com-posed of clinker produced by burning the limestone in a rotational furnace and by grinding in a ball mill. Portland cements of this type are distinguished by open matrix, and the microstructure of the products based on such binding materials is porous. Materials produced by using this binding material have larger gas penetratability, and liquids penetrate easier.

Fig 2. Structure of Portland cement grains

0

20

40

60

80

100

120

0,3

0,9

1,5

2,4

3,6

5,3 8 13 19 28 40 60 85 130

190

280

460

Diameter, µm

Cu

mu

lati

ve v

alu

es,

%

Fig 3. Particle size distribution of the Portland cement grains

According to results of the analysis of granulometric

composition (Fig 3), the size of the particles of Portland cement analysed varies from 0.3 to 140 µm. The distribu-tion of the particles depending on their size is uneven, the size of 50 % of particles of Portland cement is 7 µm and smaller. The sizes of other 40% particles vary from 7 µm to 50 µm. The remaining particles (10%) are larger than 50 µm.

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Fig 4. Microstructure of the waste catalyst grains

Fig 4 shows a scanning electron micrograph of cata-

lyst waste, which indicates that catalyst particles are spherical. The granulometric composition of the catalyst waste is showed in Fig 5.

0

0,2

0,4

0,6

0,8

1

1,2

0,04 0,5

1,1 2

3,2

4,6 7 11 17 23 36 53 75 112

170

240

400

Diameter, µm

Cu

mu

lati

ve v

alu

es,

%

Fig 5. Particle size distribution of the catalyst waste

During the analysis of the granulometric composi-

tion (Fig 5) it can be noticed that the size of particles of catalyst waste varies from 0.2 to 112 µm. Major part of the particles of this material has larger diameter than the ones of the Portland cement (Fig 3), size of 80% of the particles in the used catalyst varies from 30 µm to 112 µm. When particles of the used catalyst are compared with the particles of binding material (Green Cement Technology), it can be noticed that the particles of the catalyst are similar to the ones of the pozzolanic cement (where volcanic ash is used for the production). Both have the same shape, but the latter have 4 times smaller diameter. Specific surface area of the particles (showed in Fig 5) of used catalyst is smaller than the one of Portland cement in Fig 3.

Considering the results of microstructure and X-ray analysis of used catalyst, it can be stated that this material can replace a part of the binding materials and behave as an active mineral additive.

Microstructure analysis of the surface of coarse ag-gregate – 2–4 mm fraction expanded-clay was carried out. In Fig 6 the microstructure's photo of the surface of grain of expanded-clay is provided.

Fig 6. Microstructure of the expanded-clay grain

The statement that there are little pores in the surface

of the expanded-clay is confirmed in Fig 6. In this figure it can be noticed the diameter of pores is very small, from 5 µm to 60 µm, and the largest surface area of expanded-clay is occupied by agglomerated clay minerals. Cement stone should adhere firmly to this agglomerated and rough surface. In order to get more detailed view of ex-panded-clay pores (to verify whether they are closed or open), the image of expanded-clay pore was zoomed in (enlargement of the view of pore located in the centre of Fig 6). After more exhaustive analysis of expanded-clay pores we can notice (in Fig 7) that the internal micropores of expanded-clay are not closed. Therefore, the statement that water does not reach them, as it is stated in reference (Gailius et al. 2009), cannot be confirmed. It can be seen that the structure of pores on the surface of expanded-clay is similar to the pore structure of foam glass. Water passes into the expanded-clay through this structure of the adjacent pores. However, the number of these pores is not high, and the internal part of the expanded-clay is dominated by closed pores and capillaries. During the selection of the required amount of water for the mixture of expanded-clay lightweight concrete it must be consid-ered that the additional amount of water would be re-quired to pour into the mixture to moisten the surface of the expanded-clay granules. However, during the harden-ing this amount of water would be returned gradually to the cement stone.

Fig 7. Microstructure of the expanded-clay pore

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3.2. Microstructure analysis of the structure of hardened expanded-clay lightweight concrete

Optical microscope was used to analyse the internal structure of the samples. The following location of the hardened product was selected: contact area of the used catalyst with the formed cement stone. After the analysis of contact location of catalyst waste with the cement stone (after 2 days of hardening period), it can be noted (Fig 8) that granule of the catalyst is adhered firmly to the formed cement stone and fragmentation occurs through the cement stone. Catalyst's granule is not over crystal-lised itself, its structure remains unchanged. However, its surface has formed firm bonds with the newly formed minerals of the cement stone. These bonds are stronger than the granule's extraction force. During the compres-sion of the sample of expanded-clay lightweight concrete, when tension appears, at first, bonds break between the newly formed minerals of cement stone, but not between the catalyst and cement stone. The compressive strength of our expanded-clay lightweight concrete analysed is 5.1 MPa after 2 days of hardening.

Ageev et al. (1963) probed that when the amount of cement is altered from 315 kg/m3 to 533 kg/m3, cubic compressive strength increases by 46%. Bulk density of expanded-clay varied in a range from 325 kg/m3 to 700 kg/m3. The increase of expanded-clay density by 115 % determines the increase of cubic compressive strength of the samples by 67 %. The decrease of the amount of expanded-clay determines the increase of cu-bic compressive strength of the samples by 233 %. When the amount of expanded-clay is decreased, the compres-sive strength increases by 1.6 times. The main factor determining compressive strength and deformability of the expanded-clay lightweight concrete is the density of expanded-clay and expanded-clay lightweight concrete. The density of our analysed expanded-clay lightweight concrete after 2 days of hardening is 1596 kg/m3, and after 28 days of hardening – 1569 kg/m3. This can be explained by the fact that in former case 30% of the cata-lyst (comparing to the amount of cement) was used.

Fig 8. View of adhered catalyst waste and cement stone (where: 1-cement stone; 2-catalyst)

In order to get more detailed view of cement stone in

the contact area, its view was zoomed in (Fig 8). Results of the analysis with electronic microscope show that in

early cement's hardening stages together with ettringite the syngenite is created, which fragments later. Further, during hydration, needle C-S-H microcrystals (Fig 9) are created within 24 hours. Due to their optimal spacial arrangement and adherence, they form the core of the strength of cement stone (Sasnauskas et al. 2001).

Fig 9. View of formed C-S-H microcrystals

After 28 days of hardening, the results of the ana-

lysed contact area between expanded-clay granule and cement stone show (Fig 10) that expanded-clay granule is fully adhered (through its full surface) to the newly formed mass of cement stone, and large surface pores of the expanded-clay are filled with the minerals of cement stone. Adherence strength between expanded-clay gran-ule and cement stone is larger than the strength of ex-panded-clay granule, and, during the compression, the sample fragments through the coarse aggregates and ce-ment stone. Sand grains are adhered to the cement stone completely in other way. Sand in such conventional hard-ening conditions does not create strong bonds on its sur-face. Cement stone, existing in the contact area between sand and cement stone, at first looses contact with the surface of sand grain. In order to improve the contact strength between these materials, the hydrothermal hard-ening conditions should be maintained. Chemical bonds between sand and cement stone can be created only after the processing in autoclave and after mechanical activa-tion of the surface. The compressive strength of our ex-panded-clay lightweight concrete analysed after 28 days of hardening is 19.91 MPa.

Fig 10. Photo of microstructure of contact area be-tween expanded-clay granule and cement stone (where: 1-cement stone; 2-expanded-clay)

1

2 1

2

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Conclusions

Grains of the fine-grained catalyst waste are larger than the particles of Portland cement, and their shape is spherical (contrary to Portland cement). Size of 80 % of the particles in the used catalyst varies from 30 µm to 112 µm. Catalyst waste analysed belongs to the group of zeolites. After the X-ray structural analysis it was identi-fied that it is faujasite.

The size of Portland cement particles varies from 0.3 to 140 µm, 50% of Portland cement articles have size of 7 µm. When particles of used catalyst are compared with the particles of binding materials, we can notice that cata-lyst particles are similar to the particles of binding mate-rial. They are of the same shape, but the diameter of the latter ones is 4 times smaller. The amount of sand parti-cles with the size from 1 to 0.5 mm in the mixture is equal to 46.73 %, from 4 to 2 mm – 30.2 % and from 0.25 to 0.125 mm – 20.16%. The size of the particles of coarse aggregate is 2–4 mm.

Considering the results of microstructure and X-ray analysis of used catalyst, it can be concluded that this material can replace a part of binding materials and be-have in the formation mass as an active mineral additive.

The contact in the expanded-clay lightweight con-crete between the catalyst waste, granule of expanded-clay and cement stone is strong. During the compression of the samples, coarse aggregates and cement past start to break after 28 days of hardening.

Acknowledgements

The authors are grateful for the support of this work by the Forensic Science Centre of Lithuania Gabrielė Juodkaitė-Granskienė, Vytautas Jonaitis and Jonas Mincevičius.

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