Introduction

Lorestan province due to natural minerals and 450 factories of decorative stone in Iran is considered one of the poles in this industry. Unfortunately, the 60 % of mining stone has become lesions of stone factory (LSF) because the applied method is traditional. This problem is one of the considerable environmental issues in suburban of this province (Fig. 1).

Fig. 1
figure 1

The lesions of stone factory in and around Doroud city

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The seasonal precipitation in these industrial cities is acidic which causes the dissolution of heavy metals of these lesions infiltrating them to groundwater, agricultural land that lead to bioaccumulation in food chain [1–3]. Despite these damages in suburban area, destruction of many plant species in these areas causes soil degradation.

In addition to the environmental risks of these lesions, another reason for recycling them is the loss of mineral resources [4, 5]. The aim of this study is to find a method for removal and recycling of mentioned lesions, for instance artificial stone production.

The lesions as seen in Fig. 1 include unusable broken stones that are (with the dimensions of less than 10 cm × 10 cm) wastes of cutting of mining stone and sludge produced from cutting and polishing the stone.

Type of stone, composition and their chemical properties are important factors in the recycling. Lesions mainly include travertine and marmarit stone with the following properties:

  • Travertine stone is a sedimentary limestone and porous calcite layer that is pretty crystalized and Travertine is a natural stone such as Marble, Granite, Onyx, Limestone, Slate and so on. The key difference between Travertine and other natural stones lies in the formation of the rock, the hardness of the stone and the appearance. Travertine is formed in hot springs and/or limestone caves [6, 7].

  • Marmarit or Gohari stone is metamorphosed limestone under high pressure and heat conditions. In these metamorphic crystals, tiny crystals are re-crystallized toward coarser kinds. There are some veins in the marmarit including impurities in the original limestone [8].

The artificial stone of lesions in stone factory is produced by different formulations. Presence and absence of water pool, compressive strength and flexural tests are the factors that are measured in produced samples. To improve the properties of the produced artificial stone, fillers such as titanium dioxide (TiO2) and zinc oxide (ZnO) are added or mixed separately.

TiO2 as photo-catalyst is most widely used in different ways, in water treatment, air purifier, lubricants, anti-bacterial disinfectant, food industry, paint industry, paper manufacturing, oil and construction materials [9–11].

Titanium dioxide (TiO2) has three different crystalline structures consisting of Anatase, Rutile and Brokit. Anatase makes the stone surface beautiful. For its self-cleaning behavior, TiO2 is used in building materials and structures [12–16] including cement mortars, exterior tiles, paving block, glasses, paints, finishing coating and concrete pavement. Zinc oxide (ZnO) is a yellowish white powder and very soft with high specific surface area  which improves the surface properties and other parameters of physical chemistry [17].

Materials and devices

TiO2 and ZnO are the products of MERK. Portland cement type II: This kind of cement has average properties, is means that setting time is low and is resistant to  sulfate compounds, in this type of cement, amounts of tri-calcium silicate and di-calcium aluminates decreases and increases di-calcium silicate [18]. Other materials include: unsaturated polyester resins, micro-silica powder, Si, lesions of stone factory are the products of MERK.

Required instruments in this study include press or kicker, mixer, water meter or meter setting (JOINT STARS GROUP LIMITED) and templates with sizes: 5 × 5 × 5 and 16 × 4 × 4 cm3. Finally, sieves with mesh sizes 8, 10 and 200 were used. The smaller the sample size, the larger is the mesh size.

  • The size of drop meshes of sieve 200 → 0.0075 mm = 74 micron = 0.0029 in.

  • The size of drop meshes of sieve 10 → 2 mm = 2000 micron = 0.0787 in.

  • The size of drop meshes of sieve 8 → 2.38 mm = 2380 micron = 0.0937 in.

Light microscope with Abbe condenser, N.A. of 1.25 and adjustable aperture (aperture center can be adjusted) was used. Electric components were: input voltage AC85–265 V, 50/60 Hz, output voltage DCI.2–6 V. 6 V/20 W halogen lamp rotation potentiometer with power switch fuses 2A 5 × 20 was used.

The compressive strength was evaluated using a product of Toni Technik Germany, device number PR41004 with the following specifications: serial number 1543-03, pressure 288 bar, piston stoke 60 mm, diameter of piston 115 mm, Toni Technik Gmbh—Gustav-Meyer-Allee 25, D-13355 Berlin.

The flexural strength was evaluated using a product from Toni Technik Germany RB421002 with the following characteristics: serial number 2061-03, pressure 125 bar, piston stroke 30 mm, diameter of piston 32 mm, Toni Technik Gmbh—Gustav-Meyer-Allee 25, D-13355 Berlin.

Experimental methods

For test of samples are used templates with sizes: 5 × 5 × 5 and 16 × 4 × 4 cm3 and drop meshes of sieve size 10–200. According to formulation of Table 1, the composition of artificial stone base was determined. The amount of cement in artificial stone  should be considered to stone seeds and the amount of other materials to be determined ratio to amount of cement. Notably, the mixes or formulations of the samples are selected according to the ACI 211.1-91 Standard America [19].

Table 1 The formulation of composition of artificial stone base
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Methods of preparation of artificial stone

Initially the cement is weighed and it was equivalent to 50 % by weight of stone seeds, and water is 20–30 wt% of cement. Then water and cement were mixed into blender for 1 min at low rpm. After that we added stone seeds, unsaturated resin and filler (7 wt% micro-Si or calcium carbonate for minimize pores) to mixture of water and cement and then mixed for 1.5 min at high rpm. The mixture is ready for molding.

The molding method of artificial stone

After cleaning the templates, we installed them on kicker device. A layer of the mixture is poured into templates and the kicker machine is turned on, and 60 hits are to be imported. The second layer is poured and after 60 hits the mixture is set to air leak. Then, templates are kept in a humidity bath (θ = 30 °C and ω = 90 %) for 24 hours and are opened; the samples are put in the pool water at 20 °C for different time periods (3, 7 and 28 days). Unlike concrete, composite showed better resistance in absence of water as shown in Table 3.

Table 2 The mechanical properties of artificial stone from stone lesions with 10–200 mesh in different combination
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Compressive strength test

The UK test according to standard BS EN 12390-1: 2000 and BS EN 12390-2: 2000 are performed [20]. After drying, the templates under compressive strength test are divided into two pieces for which t 1 and t 2 were the initial and final time, respectively, and compressive strength is calculated using the below formula:

$$P({\text{kN}}) = \frac{{t_{1} - t_{2} }}{2} \times 6.37$$
(1)

Unit of compressive strength is kN and for conversion of kN to kg cm−2, units are multiplied by a constant 6.37.

Flexural strength test

The tensile strength test and applied axial tension were taken for the samples. Due to the shape of templates, there is a problem with the force being exerted in line with the axis. The tensile strength is calculated by indirect methods using the bending test and the splitting (split-half); it is according to standard BS EN 12390-5: 2000, and was conducted using the flexural strength[21, 22].

Results and discussions

At first, the samples were prepared by basic formulation: 450 g lesion of travertine stone with 10–200 and 8–200 mesh of stone seeds, 50 wt% of cement, 1.5 wt% of resin and 30 wt%. After 2–4 h, the samples are transferred to water pool for 24 h. The samples were porous and water absorption was high, so the samples did not show any resistance in compressive strength device (Table 2).

In the next sample, resin is increased up to 10–12 wt% and water is decreased to 20–25 wt% resulting in porosity decrease and increased compressive and flexural strength. The suburbs of samples are eaten and optical microscope does not show photograph, as related results are shown in Table 2. Table 3 shows the samples from lesions of TS and MS prepared in the presence and absence of water pool. The mechanical properties of dried samples in the absence of water pool are better. The TS stone seeds show less porosity and higher strength than the MS stone seeds. Flexural strength shows a significant increase in the absence of water for TS stone seeds.

Table 3 The mechanical properties of artificial stone from stone lesions with 10–200 mesh in the presence and absence of water
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To reduce the porosity of samples, cement is increased up to 70 wt% of stone seeds in TS and MS. The fillers (micro-Si and CaCO3) are added up to 5 wt% of cement. In Table 4 is shown their formulation and the samples were dried in the absence of water pool, samples containing calcium carbonate (unlike concrete) were soft and disintegrated while the samples containing micro-Si were less porous and stronger than the formulation of Table 3.

Table 4 The mechanical properties of artificial stone from stone lesions with 10–200 mesh with 7 wt% of filler equal 14.7 g
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According to the results in Table 4, the mechanical properties of this formulation are not satisfactory. The optical microscopy is a valuable method for examining the nature and progress of artificial stone and determines porosity and stone density. Figure 2 is optical microscopic images of samples with 7 wt% micro-Si for TS and MS. As is visible in Fig. 2, the dark areas show porosity in the artificial stone and the artificial stone of TS lesions is less porous.

Fig. 2
figure 2

The optical microscope images of the artificial stone with 7 wt% micro-Si

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In next step, micro-silica, TiO2 and ZnO are used as fillers in formulation. Table 5 includes the mechanical properties of these samples for which the filler content is 3 wt% of cement for TiO2, ZnO and a mixture of both. The samples containing titanium dioxide have a smoother and glossier surface than zinc oxide and a mixture of both; also the compressive strength of samples with TiO2 is better and their setting time is lower.

Table 5 The mechanical properties of artificial stone from stone lesions of TS and MS with 10–200 mesh and TiO2 and ZnO fillers
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The samples made of a mixture of titanium dioxide and zinc oxide are better than zinc oxide, but all samples with formulation of Table 5 shows better mechanical properties with the passage of time. To increase of mechanical properties, we reduced TiO2 and ZnO fillers to 1 wt% of cement as well as increased micro-Si and silane to 7 and 1 wt% of cement, respectively. The results are shown in Table 6. With the increase of micro-Si and silane to formulations of artificial stone, the surfaces have been smoother and shinier than formulations of Table 5, the optical microscopic images of which are shown in Fig. 3.

Table 6 The mechanical properties of artificial stone from stone lesions of TS with 10–200 mesh and TiO2, ZnO, micro-Si and silane fillers
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Fig. 3
figure 3

The optical microscope images of the artificial stone of TS lesions with fillers such as: micro-Si, silane and a TiO2, b ZnO and c mixture of TiO2 & ZnO

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As is visible in Fig. 3a, c, porosity of the samples containing titanium dioxide is less but the samples have smooth surface. The artificial stone of TS with TiO2 is denser because components of travertine stone formed a strong bond with the filler material (TiO2) and is of low porosity. Chemical analyses of travertine stone waste of cutting factory to produce synthetic artificial stones are done for: CaCO3, SiO2, FeS2, MgCO3, clay (Al2O3 and Fe2O3), sulfate and organic materials [23]. By comparing Figs. 2 and 3, it can be seen that fillers titanium dioxide and zinc oxide are better in forming crystalline structure and enhance the properties of artificial stone.

The mechanical properties of the samples containing 3 wt% of TiO2 or ZnO (Table 5) are more than 1 wt% of them (Table 6). Comparing the Tables 5 and 6, the compressive and tensile strength increase with addition of these fillers.

Conclusion

The aim of this study was conversion of stone factory lesions to artificial stones and recycling of these lesions. The results show mechanical properties of the prepared artificial stones with lesions of travertine stone (TS) are better than lesions of marmarit stone (MS). As a result, the percentage of TS lesions in waste of factories has direct relation with properties of produced artificial stones.

Unlike concrete, the compressive and tensile strength of artificial stone was better under exposure to air and without the presence of water pool and CaCO3 would be prepared to soften artificial stone. Titanium dioxide and zinc oxide as the fillers increased the mechanical properties and porosity of the samples. With increase of titanium dioxide, mechanical properties of artificial stone show a significant increase and these properties are increased with the passage of time.