Massive limestones were used in construction of ancient Egyptian tombs, temples, obelisks and other sculptures. These stones are always exposed to physico-mechanical deterioration and destructive forces, leading to partial or total collapse. The task of reassembling this type of artifacts represents a big challenge for the conservators. Recently, the researchers are turning to new technologies to improve the properties of traditional adhesive materials and techniques used in re-assembly of broken massive stones. The epoxy re sins are used extensively in stone conservation and re-assembly of broken stones because of their outstanding mechanical properties. The adding of nanoparticles to polymeric adhesives at low percentages may lead to substantial improvements of their mechanical performances in structural joints and massive objects. The aim of this study is to evaluate the effectiveness of montmorillonite clay, calcium carbonate, and silicon dioxide nanoparticles for enhancing the performances of epoxy adhesives used in re-assembly of archaeological massive limestones. Scanning electron microscopy (SEM) was employed in order to investigate the morphology of the prepared nanocomposites, and the distribution of nanoparticles inside the composites. Artificial aging, tensile, compressive, and elongation strength tests were used to evaluate the efficiency of epoxy-nanocomposites. The results showed that the epoxy-clay nanocomposites exhibited superior tensile, compressive, and elongation strength, in addition to improving the mechanical properties of stone joints.
Large stone carvings were use in the construction and construction of many historical Pharaonic buildings such as (tombs, temples, obelisks, etc.) [
The mentioned problems and drawbacks in epoxy materials have attracted significant academic and industrial interest to increase the efficacy of the conventional methods to achieve higher adhesive and protection efficiency [
The current study divided into two parts: Part 1: The experimental study. This part is designed to evaluate the effectiveness of the above mentioned nanoparticles in improving the properties of epoxy resins used in conservation of massive stone artifacts. The study aims to investigate the efficiency of selected nanocomposites in re-assembly of massive archaeological stones and identify the best of these nanocomposites for dealing with such types of stone monuments.
The obtained nanocomposites were prepared using mechanical methods, and characterized using Scanning electron microscopy (SEM) to evaluate the surface morphology and the homogeneous distribution of filler nanoparticles in the polymer matrix. The obtained epoxy-nanocomposites were casted in form of epoxy molds, and were applied as adhesive material for experimental stone samples. The behavior of the nanocomposites exposed to artificial aging was investigated. The mechanical properties were determined for both the epoxy molds and experimental stone samples with and without artificial aging.
Part 2: The applied study. This part will be a continuation of the experimental study that were carried out in part 1, the applied study represents a big project was carried out on 3 archaeological massive stones discovered separately in Ain Shams (Heliopolis) archaeological area (see
The epoxy resin used as a matrix was PY 1092-1 (100 part by weight) and its hardener HY 1092 (45 part by weight). It was purchased from (Huntsman Advanced Materials Ltd, Basel, Switzerland), commercially known as Araldite® Precision. The weight ratio of the epoxy resin to the hardener was 2:1.
The montmorillonite Organo-modified Nano clay (cloisite 30B), CaCO3 Nano powder (NPCC 201), and SiO2 nanoparticles (S-type, Spherical, Nonporous, and amorphous) with particle diameter average < 50 nm, were produced and characterized by Nanografi Nanoteknoloji company—Ankara, Turkey and the data sheet supplied by the company provided with all information about the nanomaterials properties and size.
The experimental limestone blocks (samples) were collected from the quarry of Helwan plateau in the south part of greater Cairo, one of the most important limestone quarries in Egypt. Ain Shams, Heliopolis, and Mataria monuments were constructed mainly from Helwan and Abu Zaabl local limestone quarries. Experimental limestone blocks were cut into rectangular samples (10 cm × 2 cm × 2 cm) for carrying the mechanical tests such as Tensile and elongation strength tests. The used limestone samples were compatible with the chemical composition of the original material of studied archeological limestone blocks (Part 2). Afterwards, the samples were prepared for applying the studied nanocomposites adhesives by cleaning the surface by soft brush, then washed using distilled water, and dried in an oven at 105˚C [
There are many methods to prepare polymer-nanocomposites whether chemical or mechanical methods. However, according to the properties of epoxy resin and its high viscosity, the mechanical method was most suitable mixing epoxy resin with nanoparticles in order to form intercalated nanocomposite ensures the distribution of nanoparticles within the epoxy resin evenly and uniformly. In this regard, Epoxy nanocomposites are usually prepared by dispersing nanoparticles (Clay, CaCO3, and SiO2) into the epoxy matrix without hardener and the epoxy resin were mixed with nanoparticles content 3% (w/v), and mixed well with a glass rod before subjected to mechanical stirring at 500 rpm for 1 h. Then, the mixture was held at 70˚C - 80˚C and stirred again at 2500 rpm for 1 h with a high-shear mixer. The mixed compositions were mechanically blended and sonicated for 2 h with a little heating to ensure the distribution of nanoparticles within the epoxy matrix with no clustering or agglomeration of nanoparticles [
The surface morphology and fracture surface of the obtained epoxy nanocomposites were investigated using SEM in order to investigate if filler nanoparticles were distributed homogenously and do not form aggregates in the epoxy polymer matrix (The SEM investigation were carried out in FEG Lab; the Egyptian mineral resources authority, Cairo, Egypt).
After preparing the epoxy nanocomposites, the appropriate amount of hardener according to the above-mentioned mixing ratio (2:1) was added and mixed well. Afterwards, the obtained compositions (Resin, hardener, and nanoparticles) were casted in mold with special frame made from steel with dimensions (10 cm × 2 cm × 1 cm) and (2 cm × 2 cm × 1 cm), and were left to dry for 24 h to be ready for carrying the mechanical evaluation tests (See
The obtained adhesive nanocomposites (Resin, hardener, and nanoparticles) were applied as adhesive materials to assembly of experimental limestone samples by joining each two samples together at room pressure and temperature. The joined samples were left to dry for 24 h at room temperature with controlled RH 50%, the time set for epoxy nanocomposites to achieve full dryness (See
Epoxy molds samples and assembly experimental limestone samples were subjected to artificial aging tests, with aim of simulating the actual environmental deteriorating conditions and at quantifying the durability of the adhesive materials. Two types of weathering cycles were performed as follow:
1) Salt crystallization weathering
The experimental samples were subjected to ten cycles of immersion in a saturated Na2SO4 solution for 4 h followed by 28 h of exposure to air in normal room conditions (25˚C and 40% R.H.) then 16 h in an oven at 70˚C [
2) Wet-dry cycles
This test was carried out with the aim of evaluating the stability of the adhesive materials against thermal effects. The test consists of 40 cycles of immersion and drying as follows: 16 h of total immersion in distilled water then 8 h in an oven at 70˚C [
The mechanical properties of tested nanocomposites adhesives were conducted for both epoxy molds samples, and assembly experimental limestone samples, before and after artificial aging to evaluate its long-term durability against different mechanical forces. Therefore, three types of mechanical tests mentioned below were conducted.
1) Tensile and elongation strength measurement
Tensile and elongation strength were measured according to ASTM D 412-66 using an electronic tensile testing machine (Zwick 1425). Tensile test was performed at a crosshead speed of 10 mm/min, and was calculated by using the following equation: Tensile strength (TS) = (F/tw) MPa, where F = load applied to rupture, t = the thickness of the specimen and w = width of the specimen. At the break, the elongation is expressed as the percent of the original benchmark length attained beyond rupture.
Ultimate elongation E% = ((L − L0)/L0) 100, Where: L = Length of the specimen at the moment of rupture and L0 = the length between bench marks [
2) Compressive strength measurement
Compressive strength was performed on the epoxy molds samples using an Amsler compression-testing machine, with the load applied perpendicular to the bedding plane according to ASTM C 170 standard (1976). For each compound, 3 samples were tested, and the average values of compression strength were recorded [
SEM characterization methods were employed to investigate microstructure, morphology, and mixture process of the prepared epoxy-nanocomposites. SEM images of the control resin (pure epoxy, containing no nanoparticles) and the epoxy nanocomposites are shown in (Figures 4(a)-(d)). SEM image in (
transparent compared to traditionally filled composites. Epoxy-nanocomposites with high content of nanoparticles can induce nanoparticles agglomeration, and more difficultly in the procedures of mixing and applying [
Measurement of compressive strength was performed on all of casted epoxy molds samples, whether the pure epoxy and epoxy-nanocomposites before and after artificial aging. The test was performed based on the ASTM C 170 standard in order to investigate the effect of adding different nanoparticles on the mechanical performance of epoxy-nanocomposites. For each compound, at least 3 samples were tested and the mean values were considered. The compressive strength tests results of various nanocomposites are indicated in
The results also showed significant effectiveness of the modified CaCO3 nanoparticles as a filler material for the epoxy composites, which comes in second class after clay nanoparticles. The results confirm the reinforcement effect of calcium carbonate nanoparticles in epoxy matrix, when incorporated in low contents due to their high surface contact area which is a result of the small particle diameter, also the strong interaction between the polymer and filler, because of the large interfacial area between them. Addition of rigid particles to a polymer matrix can easily improve the polymer properties since the rigidity of inorganic fillers is generally much higher than that of organic polymers.
Tests of tensile and elongation strength were measured according to ASTM D 412-66 standard. The measurements of tensile strength were performed on both of casted epoxy molds samples and assembly of experimental limestone samples before and after artificial aging. For each compound, at least 3 samples were tested and the mean values were considered. From the tensile test, results of neat epoxy and its nanocomposites as presented in
Samples | Compressive Strength of Epoxy-Nanocomposites Samples | |||||
---|---|---|---|---|---|---|
Before Artificial Aging | After Artificial Thermal Aging | After Artificial Salt Weathering | ||||
Average Value (kg/cm2) | Change % | Average Value (kg/cm2) | Change % | Average Value (kg/cm2) | Change % | |
Pure epoxy | 125.53 | 0.00 | 120.60 | −3.92 | 124.11 | −1.13 |
Clay/epoxy nanocomposites | 133.89 | +6.65 | 131.22 | −1.99 | 133.11 | −0.58 |
CaCO3/epoxy nanocomposites | 129.84 | +3.43 | 126.84 | −2.31 | 128.98 | −0.66 |
SiO2/epoxy nanocomposites | 127.80 | +1.80 | 123.40 | −3.44 | 126.88 | −0.71 |
Samples | Tensile Strength of Epoxy-Nanocomposites Samples | |||||
---|---|---|---|---|---|---|
Before Artificial Aging | After Artificial Thermal Aging | After Artificial Salt Weathering | ||||
Average Value (Mpa/TS) | Change % | Average Value (Mpa/TS) | Change % | Average Value (Mpa/TS) | Change % | |
Pure epoxy | 19.59* | 0.00 | 17.66 | −9.85 | 18.11 | −7.55 |
Clay/epoxy nanocomposites | 28.53 | +45.63 | 27.60 | −3.25 | 28.22 | −1.08 |
CaCO3/epoxy nanocomposites | 25.56 | +30.47 | 23.27 | −8.95 | 24.06 | −5.86 |
SiO2/epoxy nanocomposites | 210.47 | +9.59 | 29.21 | −10.52 | 20.01 | −6.80 |
Samples | Tensile Strength of Assembly Stone Samples | |||||
---|---|---|---|---|---|---|
Before Artificial Aging | After Artificial Thermal Aging | After Artificial Salt Weathering | ||||
Average Value (Mpa/TS) | Change % | Average Value (Mpa/TS) | Change % | Average Value (Mpa/TS) | Change % | |
Pure epoxy | 33.66 | 0.00 | 31.13 | −7.50 | 32.01 | −4.90 |
Clay/epoxy nanocomposites | 42.76 | +27.03 | 41.50 | −2.94 | 42.10 | −1.54 |
CaCO3/epoxy nanocomposites | 38.89 | +15.53 | 36.88 | −5.16 | 37.88 | −2.59 |
SiO2/epoxy nanocomposites | 35.32 | +4.93 | 33.11 | −6.25 | 34.09 | −3. 48 |
Samples | Elongation Strength of Epoxy-Nanocomposites Samples | |||||
---|---|---|---|---|---|---|
Before Artificial Aging | After Artificial Thermal Aging | After Artificial Salt Weathering | ||||
Average Value % | Change % | Average Value % | Change % | Average Value % | Change % | |
Pure epoxy | 9.37 | 0.00 | 7.63 | −18.56 | 8.89 | −5.12 |
Clay/epoxy nanocomposites | 18.42 | +96.58 | 17.49 | −5.04 | 17.99 | −2.33 |
CaCO3/epoxy nanocomposites | 14.18 | +51.33 | 13.61 | −4.01 | 13.89 | −2.04 |
SiO2/epoxy nanocomposites | 11.61 | +23.90 | 10.23 | −11.88 | 10.76 | −7.32 |
This study focused on reassembling archaeological massive limestones using epoxy resin (Araldite 1092) modified with nanomaterials. In this study, montmorillonite clay, CaCO3, and SiO2 nanoparticles were added to epoxy resin in order to improve its physiochemical and mechanical properties and identify its ability to use in re-assembly of massive stone monuments. The study showed that the low content of nanoparticles (3% w/v) is appropriate to mix and intercalated well with high viscosity of epoxy. The results obtained by mechanical tests (compressive, tensile, and elongation strength) indicated that clay nanoparticles were the best nanomaterial which filled the epoxy matrix, and gave the highest values of mechanical properties before and after artificial aging compared to pure epoxy sample and epoxy mixed with CaCO3 or SiO2, followed by CaCO3 nanomaterial. Therefore, the study recommends the use of epoxy-clay nanocomposite in the case of reassembly of archaeological massive limestones, which will be applied in part 2 of the study.
The authors would like to express their gratitude sincere to King Abdulalziz City for Science and Technology (KACST), Riyadh, Saudi Arabia for the valuable and continuous scientific and moral support.
Sawsan S. Darwish, Sayed M. Ahmed, and Mohammad A. Aldosari conceived and designed the experiments; Sayed M. Ahmed and Mahmoud A. Adam performed the experiments; Sawsan S. Darwish, Nagib A. Elmarzugi, and Mahmoud A. Adam analyzed the data; Mohamed A. Aldosari and Nagib A. Elmarzugi contributed reagents/materials/analysis tools; Sawsan S. Darwish, Mahmoud A. Adam and Sayed M. Ahmed wrote and review the paper.
The authors have no conflicts of interest to declare.
Aldosari, M.A., Darwish, S.S., Adam, M.A., Elmarzugi, N.A. and Ahmed, S.M. (2020) Re-Assembly of Archaeological Massive Limestones Using Epoxy Resin Modified with Nanomaterials—Part 1: Experimental. Green and Sustainable Chemistry, 10, 24-38. https://doi.org/10.4236/gsc.2020.101003