Protection of Limestone Coated with Different Polymeric Materials

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Table 2. Chemical Composition of coated materials

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Figure 1. XRD analysis of historical limestone one sample of Thebes mountain

Table 3. EDX analysis results for Thebes limestone near HASEBSHOUT temple (ms%)

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Figure 2. EDX analysis of historical limestone of Thebes mountain

4. Experimental Work

The as received limestone of (30 mm ×30 mm ×30 mm) is tested in compassion using computerized universal testing machine (model WDW-100) at 1mm/min crosshead speed. Four groups of tested specimens are coated by chemical material Paraloid 44 (B44), Paraloid 72 (B72), ethyl silicate and Wacker OH100. The coating process is performed by immersion of limestone specimens into the coating chemicals for 72 hr. for each. The limestone coated with the various solvent and that without coating are immersed in salty groundwater path for 15 days continuously. The density of the as received and chemically treated rocks is measured. Moreover, the porosity and water absorption are calculated according ASTM- D1037-06a ^[26] using Eq. 1. The compression test is carried out according to ASTM D2938-95 ^[27].

(1)

where, is the final weight after soaking for 72 hours and is the initial weight.

5. Results and Discussion

5.1. Microstructure Examination

Figure 3 shows SEM photographic examination. It is clear that Paraloid B44 has a thick layer with voids and pores appeared. Partially distribution in the surface structure of limestone (see Figure 3 a). In (Figure 3 b) thick film and dense distribution of Paraloid B72 are closing of the stone. For Wacker (OH 100) good penetration in homogeneous form with the internal structure of limestone as in Figure 3-C, while, ethyl silicate (ESL) has many voids and pore which weaken the coating efficiency (see Figure 3-d).

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Figure 3. SEM analysis of polymer coating homogeny distributed

5.2. Compressive Strength

Figure 4 shows a compressive stress-strain diagram of treatable surfaced limestone. It clearly appears that limestone coated with Paraloid (B44) and Wacker (OH 100) has good adhesive and strength than other coating polymers (clearly shown in Figure 6). This is due to highly uniformly distribution of (B44) and (OH100) see Figure 3. The flow curves of the most tested specimens are not smooth; this can be attributed to macrocracks emanating during the action of compression load. The enhancement of strength for all specimens with respect to the untreatable limestone (as-receive) are listed in Table 4 and Table 5 and they are illustrated clearly in Figure 7 which gives a percent of increase of nominal strength () with each coating agent. Figure 5 shows compressive stress-strain diagram after the immersion of the treatable and untreatable limestone in salinity water path. The presence of Gypsum (CaSO₄. 2H₂O) was created through the reactions between limestone and sulfate sources, according to the following reaction:

Ca CO₃+ Na₂SO₄ + 2H₂O → Ca SO4. 2H₂O + Na₂ CO₃.

Table 4. Enhancement with chemical coating before immersion process

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Table 5. Strength reduction with immersion action

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Figure 4. Compressive stress strain diagram for un-immersion coated limestone

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Figure 5. Compressive stress strain diagram for immersion coated limestone

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Figure 6. Comparison coating efficiency

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Figure 7. Normalized nominal strength respect to different coating

It commonly originates from the deposition in wet and dry which sulfate products, attack carbonic rocks. The availability of sodium sulfuric (Na₂SO₄) in the salinity water is the main reason for highly strength reduction of untreatable limestone (as received) when the specimen immersion in that water. While for coated ones (treatable one), the coating protects the limestone from a directly reaction. Therefore, the specimen resists the chemical action with different grade according to types and amount of coating and their diffusion and distribution over the limestone surface. It is clearly illustrated that Paraloid B44 and Wacker OH100 have more stability under salinity water. The strength reduction is also due to density stability of these coatings. Which is shown in Figure 8. The water absorption is enhanced with polymeric coatings of the limestone as shown in Figure 9. Figure 10 illustrates relative porosity with the coating polymer through limestone surfaced. It is clear that these polymers extended through the porosity of the limestone surface with a variety of grade. Ethyl silicate is clearly seen that it decreases with strength in both cases. This may be attributed to that Ethyl silicate is react with limestone itself forming a brittle tough material which cannot withstand the compressive load ^{[28, 29]}.

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Figure 8. Density variation with different chemical coating

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Figure 9. Water absorption variation with chemical coating

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Figure 10. Porosity enhancement with chemical coating

5.3. Weathering Failure mechanism of historic limestone

There are four modes of failure due to weathering and natural environment. These modes can be surmised to;

• Cracks “Individual fissure, clearly visible to the naked eye, resulting from the separation of one part from another” as shown in Figure 11.

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