A METHOD OF MAKING MOLDED PARTS HAVING SMOOTH SURFACE AND MOLDED PARTS MADE THEREOF

Abstract

The invention relates to a method of making parts of construction materials by using a mold coated with multiple resin-based layers comprising at least an epoxy resin-based primer and a polyurethane resin-based demolding layer, wherein the mold can be used for multiple cycles after curing and demolding. The invention also relates to the resin-coated mold and the cured parts of construction materials having smooth surface made thereof.

Claims

1. A mold for molding construction materials characterized in that the mold is coated with multiple resin-based layers comprising at least a first epoxy resin-based primer layer and a second polyurethane resin-based demolding layer.

2. The mold according to claim 1, wherein said demolding layer is coated on top of the primer layer.

3. The mold according to claim 1, wherein said epoxy resin-based primer layer contains the reaction product from a composition comprising bisphenol A epoxy resin, at least one amine-based curing agent, at least one accelerating agent and optional additives selected from the group consisting of anti-rust fillers, mica powder, pigments, defoamers, wetting dispersants, coupling agents, thickening agents and any mixture thereof.

4. The mold according to claim 3, wherein said epoxy resin-based primer layer contains the reaction product from a two-component composition comprising: (I) Component A comprising ≥50 wt. % to ≤100 wt. % by weight of Component A of bisphenol A epoxy resin; and (II) Component B comprising: (i) ≥90 wt. % to ≤99 wt. % by weight of Component B of at least one amine-based curing agent; and (ii) ≥1 wt. % to ≤10 wt. % by weight of Component B of at least one accelerating agent, wherein the weight ratio of Component A to Component B is in the range of 10:1 to 10:9.

5. The mold according to claim 2, wherein said polyurethane resin-based demolding layer contains the reaction product from a composition comprising polyol, water, polyisocyanate, metal component, and optional additives selected from the group consisting of fillers, dispersants, plasticizers, defoamers, wetting dispersants, thickening agents and any mixture thereof.

6. The mold according to claim 5, wherein said polyurethane resin-based demolding layer contains the reaction product from a two-component composition comprising: (I) Component C comprising: (i) ≥0.2 wt. % to ≤40 wt. % of a first saturated polyhydroxy compound based on the total weight of the two-component composition selected from the group consisting of polyether polyol, polyester polyol, C2 to C32 alkyl polyol and sugar alcohol; (ii) ≥1 wt. % to ≤50 wt. % of water based on the total weight of the two-component composition; and (iii) ≥2 wt. % to ≤50 wt. % of at least one metal component selected from the group consisting of metal oxide, metal hydroxide, metal aluminate and metal silicate, by weight of the total weight of the two-component composition; and (II) Component D comprising at least one polyisocyanate.

7. The mold according to claim 6, wherein Component C further comprises ≥0.2 wt. % to ≤20 wt. % by weight of the total weight of the two-component composition of a second saturated polyhydroxy compound selected from the group consisting of polyether polyol, polyester polyol, C2 to C32 alkyl polyol and sugar alcohol, wherein the second saturated polyhydroxy compound is different from the first saturated polyhydroxy compound.

8. The mold according to claim 7, wherein the first saturated polyhydroxy compound has a weight average molecular weight Mw in the range of ≥100 to ≤20,000 g/mol and the second polyhydroxy compound has a weight average molecular weight Mw in the range of ≥50 to ≤2,000 g/mol.

9. The mold according to claim 5, wherein the at least one polyisocyanate in Component D is a liquid oligomer or prepolymer.

10. The mold according to claim 5, wherein the at least one polyisocyanate in Component D is selected from the group consisting of pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 2,2,4- and 2,4,4,-trimethyl-1,6-hexamethylene diisocyanate, tetramethoxybutane 1,4-diisocyanate, butane-1,4-diisocyanate, dicyclohexylmethane diisocyanate, cyclo-hexane 1,3- and 1,4-diisocyanate, 1,12-dodecamethylene diisocyanate, diisocyanates of dimeric fatty acids, lysine methyl ester diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, hydrogenated diphenylmethane diisocyanate, hydrogenated 2,4-tolyene diisocyanate, hydrogenated 2,6-tolylene diisocyanate, methylene diphenyl diisocyanate, toluene diisocyanate, naphthalene diisocyanate, polymeric methylene diphenyl diisocyanate, and carbodiimide-modified methylene diphenyl diisocyanate.

11. The mold according to claim 6, wherein the amount of the at least one polyisocyanate in Component D is in the range of ≥10 wt. % to ≤90 wt. % based on the total weight of the two-component composition.

12. The mold according to claim 1, wherein said mold is made of metal or plywood and/or have metal or plywood contacting surface, preferably said mold is made of steel, aluminum or plywood and/or has steel, aluminum or plywood contacting surface.

13. The mold according to claim 1, wherein said primer layer has a thickness selected from ≥0.1 mm to ≤2 mm, or ≥0.1 to ≤1 mm, or ≥0.1 to ≤0.5 mm.

14. The mold according to claim 1, said primer layer has a Shore D hardness of not less than 30, or not less than 50, or not less than 70.

15. The mold according to claim 1, wherein said primer layer has an adhesion with the mold substrate of not less than 1.0 MPa, or not less than 2.5 MPa.

16. The mold according to claim 1, wherein said primer layer has a glass transition temperature of not less than 60° C.

17. The mold according to claim 1, wherein said demolding layer has a thickness of 0.1 mm to 2 mm, or 0.1 to 1 mm, or 0.1 to 0.5 mm.

18. The mold according to claim 1, wherein said demolding layer has a Shore D hardness of not less than 60, or not less than 70.

19. The mold according to claim 1, wherein said demolding layer has a contact angle of not less than 70°.

20. The mold according to claim 2, wherein said demolding layer has an adhesion to the surface of the primer layer of not less than 2.5 MPa.

21. A method for making molded construction materials, comprising the steps of: (I) adding construction materials into a mold according to claim 1; (II) curing the construction materials to form cured parts of construction materials; and (III) demolding the cured parts of construction materials from the mold.

22. The method according to claim 21, wherein step I) to III) are repeated for not less than twice.

23. The method according to claim 22, wherein step I) to III) are repeated for not less than 10 times, or more than 20 times, or more than 30 times, or more than 50 times.

24. The method according to claim 21, wherein said construction material is a concrete comprising cementitious material, aggregates, and water, wherein the weight ratio between water to cementitious material is in the range of ≥0.25 to ≤0.50, or ≥0.27 to ≤0.45, or ≥0.3 to ≤0.45.

25. The method according to claim 24, wherein said cementitious material is CEM I-V cement or geopolymer raw material.

26. Cured parts of construction material obtained from the method according to claim 1.

27. The cured parts of construction material according to claim 26, wherein the construction material is concrete and the percentage of total air voids area on the surface of the cured concrete part is not more than 0.9%, or not more than 0.8%, or not more than 0.6%, or not more than 0.5% based on the total surface area of the cured concrete part.

Description

[0192] Additional features and advantages of the invention will be more fully understood by considering the following description of examples thereof, taken in conjunction with the accompanying figures, in which:

[0193] FIG. 1 shows the demolding result of molded geopolymer concrete parts according to prior arts;

[0194] FIG. 2 shows the surface finish of molded OPC concrete parts according to comparative example;

[0195] FIG. 3 shows the surface finish of molded OPC concrete parts according to the invention;

[0196] FIG. 4 shows the surface finish of molded geopolymer concrete parts according to comparative example;

[0197] FIG. 5 shows the surface finish of molded geopolymer concrete parts according to the invention.

EXAMPLE

[0198] The present invention will now be described with reference to Examples and Comparative Examples, which are not intended to limit the scope of the present invention.

[0199] Materials and Devices

[0200] The following materials were used:

[0201] For primer:

[0202] Bisphenol A Epoxy Resin Araldite® GY 257 CI and amine-based curing agent Aradur® 450 BD were commercially available from Huntsman. Antirust filler aluminum triphosphate (CAS No. 13939-25-8), mica powder (CAS No. 12001-26-2), TiO.sub.2 powder (CAS No. 13463-67-7), silane coupling agent KH-560 (CAS No. 2530-83-8) were used. Lucramul® WT 100 was purchased from Levaco Chemicals and used as wetting dispersant. BYK-410 was purchased from BYK and used as thickener. BYK-354 was used as defoamer. 2,4,6-Tris((dimethylamino)methyl)phenol (DMP-30, CAS No. 90-72-2) was used as the accelerating agent.

[0203] For demolding layer:

[0204] Arcol polyol 1104 was purchased from Covestro and used as the first polyhydroxy compound. Glycerin was used as the second polyhydroxy compound. 4,4′-diphenylmethane diisocyanate (MDI) with a functionality of 2.7 commercially available from BASF was used as polyisocyanate. Disperbyk® 199 was purchased from BYK and used as wetting dispersant. Calcium hydroxide CL-90S was used as metal component. BYK 088 was used as defoamer. Proviplast® 1783 from Pro-viron and Hexamoll® DINCH were used as plasticizer. Fumed silica was used as thickener.

[0205] A3 #(Q235 #) steel is provided by Shanghai Yihao Mechanical Equipment Co., Ltd. and used to assemble the mold. Manol Form Remover for metal mold ( )from Manol Co. Ltd. was used as the mineral oil type demolding agent in the comparative example.

[0206] The following devices were used:

[0207] IKA mixer was used for mixing the components. BINDER was used as the heating oven for curing. PosiTector 6000 was used to measure the thickness. HTS-610D was used to measure the hardness. Dataphysics OCA was used to measure the contact angle. Posited AT-A was used to measure the adhesion. DSC was used to measure the glass transition temperature.

[0208] Measurement Methods

[0209] (1) Contact Angle

[0210] Contact angle is measured by Dataphysics OCA. 5 points of the coating surface are tested to get an average value of the contact angle.

[0211] (2) Pull-off Adhesion

[0212] Pull-off adhesion is determined according to ASTM D4541 by Posited AT-A.

[0213] (3) Hardness

[0214] Hardness (Shored D) is determined according to DIN53505 and by HTS-610D. 5 points of the coating surface are tested to get an average value of the hardness.

[0215] (4) Glass Transition Temperature

[0216] Glass Transition Temperature is determined by DSC method.

[0217] (5) Percentage of Air Voids Area

[0218] Percentage of Air Voids Area is determined by image analysis software ImageJ according to the procedure described in Example 6.

[0219] (6) Thickness

[0220] Thickness is measured by PosiTector 6000. 12 points of the coating surface are tested to get an average value of the thickness.

Example 1. Composition of Primer

[0221] According to the following general procedure, the composition as per Table 1 was prepared and later applied on the substrate of the mold.

[0222] In the respective blending proportions shown in Table 1, components of Component A and Component B were weighted and placed in a glass vessel and then mixed with an IKA mixer at speed of 1500 rpm for 1 min to obtain the primer.

TABLE-US-00001 TABLE 1 The components of primer in Example 1 Component Material Dosage* (wt %) Component A Araldite GY 257 CI 70 Aluminum triphosphate 12 Mica powder 12 TiO.sub.2 powder 5.96 Lucramul WT 100 0.01 KH-560 0.01 BYK-410 0.01 BYK-354 0.01 Component B Aradur 450 BD 98 DMP-30 2 Mix ratio (Component A:Component B) 2:1 *based on the total weight of each component

[0223] It is understood that the primer provides sufficient bonding between the substrate and the demolding layer. It can also be used as an anti-corrosion coating on steel or metal substrate. The viscosity and rheology of the primer can be further adjusted by a thickener and a rheology modifier to accommodate different conditions of the mold, e.g. application on vertical planes of the mold.

Example 2. Composition of Demolding Agent

[0224] According to the procedure in Example 1, the compositions as per Table 2 were prepared.

TABLE-US-00002 TABLE 2 The components of demolding agent in Example 2 Dosage* (wt %) Example Example Example Component Material 2A 26 2C Component Deionized Water 15 15 15 C Arcol polyol 1104 25 40 40 Glycerine 20 11 11 CL-90S 36 29.5 30 Disperbyk 199 2 2 2 BYK 088 2 2 2 Fumed silica — 0.5 — Component Polyisocyanate MDI 80 — — D Prepolymer MDI — 80 80 monomer Plasticizer Proviplast 20 20 — 1783 Hexamoll ® — — 20 DINCH Mix ratio (Component C:Component D) 30:70 44:56 44:56 *based on the total weight of each component

[0225] Monomer of 4,4′-diphenylmethane diisocyanate (MDI monomer) with NCO concentration of 31% was used in Example 21B-2C and liquid prepolymers of 4,4′-diphenylmethane diisocyanate with NCO concentration of 26% was used in Example 2A. MDI prepolymer was prepared by prepolymerization of MDI with polyol such as Castor oil.

[0226] The viscosity and rheology of the demolding layer can be adjusted by using a thickener and a rheology modifier to accommodate different conditions of the mold, e.g. application on vertical planes of the mold.

Example 3. Preparation of the Mold

[0227] Three A3 #(Q235 #) steel plates with dimension 530 mm*150 mm*2 mm and two A3 #(Q235 #) steel plates with dimension 150 mm*150 mm*2 mm were used to form the mold. The steel plates are sanded to remove any stain, oil, oxides and other residue on the surface and cleaned with ethanol.

[0228] Proper amount of primer obtained according to Example 1 was brushed on the surface of five steel plates to form a layer of 0.2 mm. The plates with the primer are then placed in the oven at 23° C. for 24 hours.

[0229] After the primer is cured, proper amount of demolding agent obtained according to Example 2 was then brushed on top of the primer thus obtained to form a demolding layer of 0.2 mm. The five plates with the primer and the demolding layer are then placed in the oven for curing at 23° C. for 24 hours.

[0230] A steel frame with dimension 530 mm*150 mm*150 mm was used to assemble steel plates to from the mold. Buffer materials were applied at the back of the plates to secure the plates in place so that only the demolding layer faced the cavity to be filled with the concrete materials. The plates were stuck at the same position in every cycle. Same mold was used in each cycle throughout the experiment. The molds prepared with plates coated with primer according to Example 1 and demolding layer according to Example 2A-2C were named Example 3A-3C respectively.

[0231] The thickness, hardness, contact angle, adhesion, glass transition temperature of the plates was tested, and the results were summarized in Table 3.

TABLE-US-00003 TABLE 3 Characterization of the plates of the mold Layer Example 3A 36 3C Primer Thickness (mm) 0.2 0.2 0.2 Hardness (Shore D) 94 94 94 Glass transition temperature 81 81 81 (° C.) Adhesion with steel plates >2.5 >2.5 >2.5 (Mpa) Demolding Thickness (mm) 0.2 0.2 0.2 layer Contact angle (°) 82 85 85 Hardness (Shore D) 75 78 78 Adhesion with primer (Mpa) >2.5 >2.5 >2.5

Example 4. Composition of OPC Concrete

[0232] According to the following general procedure, the OPC concrete as per Table 4 were prepared.

[0233] Taiheiyo Cement having a density of 3.16 g/cm.sup.3 was used as cement. Oi river sand having size <5 mm and density of 2.58 g/cm.sup.3 was used as fine aggregate (sand). Oume crush stone having size of 5-20 mm and density of 2.65 g/cm.sup.3 was used as coarse aggregates (gravel).

[0234] The OPC concrete was mixed in a pan type mixer. Sand, gravel and cement were put into the mixer to form a sandwich of sand/gravel+cement+sand/gravel and pre-mixed for 10 seconds. Water and admixture (MG8000SS) were added and the concrete was mixed for 90 seconds to obtain a uniform mix.

TABLE-US-00004 TABLE 4 The components and properties of OPC concrete in Example 4 Example 4A Example 4B Material Water 170 175 (kg/m.sup.3) Cement 420 583 Sand 839 789 Gravel 933 808 Admixture 3.36 5.25 (MG8000SS) Sand/(Sand + Gravel) (volume %) 50 50 Water/Cement (wt%) 40.5 30 Slump (cm) 21 ± 2.5 — Flow (cm) 35 ± 5   60 ± 5 Air content % 2 3

[0235] It's understood that water to cement ratio of 25-50% is preferred to obtain a OPC concrete with few air voids.

Example 5. Composition of Geopolymer Concrete

[0236] According to the following general procedure, the geopolymer concrete as per Table 5 were prepared.

[0237] Blast furnace slag with a Blaine value of 4000 cm.sup.2/g and a density of 2.91 g/cm.sup.3, type F fly ash with 54.6% SiO.sub.2 by weight and a density of 2.29 g/cm.sup.3, microsilica with 95.9% SiO.sub.2 by weight and a specific surface ratio of 18.5 m.sup.2/g were used. The alkaline activator used was a 15% strength by weight aqueous NaOH and a 10% strength by weight aqueous KOH solution. R+D SPC 2017 from BASF was used as a dispersant.

TABLE-US-00005 TABLE 5 The components and properties of geopolymer concrete in Example 5 Example 5A Example 5B Material NaOH (15%) 180 (kg/m.sup.3) KOH (10%) 305 cementitious Fly ash 300 150 material Slag 150 400 Microsilica 50 30 R + D SPC 2017 20 10 Sand 800 800 Gravel 800 800 Sand/(Sand + Gravel) (volume %) 50 50 Water/cementitious material (wt %) 29 45 Flow (cm) 55 ± 5 35 ± 5 Air content % 8 6

[0238] Geopolymer concrete was mixed in a pan type mixer. Sand, gravel, fly ash, slag, and microsilica were put into the mixer to form a sandwich of sand/gravel+fly ash/slag/microsilica+sand/gravel and pre-mixed for 20 seconds. Aqueous alkali activator solution and dispersant were added and the geopolymer concrete was mixed for 180 seconds to obtain a uniform mix.

[0239] It's understood that water to cementitious material ratio of 25-45% is preferred to obtain a geopolymer concrete suitable for curing and molding.

Example 6. Curing and Demolding OPC Concrete Parts

[0240] After reaching the required slump, flow and air content value as mentioned in Table 4, the OPC concrete obtained in Example 4A was poured into the molds obtained according to Example 3A-3C from center to side. OPC concrete was poured in two layers. Each layer being internally vibrated in four equidistant spots with high speed for 10 seconds per spot in each layer.

[0241] The molds were then covered with plastic wrap and placed in 23° C. for the OPC concrete to rest. After 2 hours of rest, the mold with concrete was placed into the BINDER chamber and cured according to the following temperature schedule for 22 hours.

[0242] Schedule 1. Increase the temperature from 20° C. to 50° C. in 2 hours;

[0243] Schedule 2. Keep the temperature at 50° C. for 3 hours;

[0244] Schedule 3. Decrease the temperature from 50° C. to 20° C. in 3 hours;

[0245] Schedule 4. Keep the temperature at 20° C. for 14 hours.

[0246] Demolding was carried out immediately after curing. Each plate was removed from the frame and the molded OPC concrete parts were demolded. The plates were then held under tap water to remove the loosely held particles. Strongly attached mortar particles were removed with the edge of a soft brush, if there is any. After all visible mortar particles were removed, the plates were wiped with a wet cloth followed by wiping with a dry cloth. This would make the plates ready for the next cycle. The molded concrete parts obtained by using mold according to Example 3A-3C were named Example 6A-6C respectively.

[0247] The plates were put back into the frame to repeat the above steps for a total of 30 cycles for Example 6A and 6C and 50 cycles for Example 6B. The plates were stuck at the same position in every cycle.

Example 7. Curing and Demolding Geopolymer Concrete Parts

[0248] After reaching the required flow and air content value as mentioned in Table 5, the geopolymer concrete obtained in Example 5A was poured into the mold obtained according to Example 3B from center to side. Geopolymer concrete was poured in two layers. Each layer being internally vibrated in four equidistant spots with high speed for 10 seconds per spot in each layer.

[0249] The molds were then covered with plastic wrap and placed in 20° C. for the geopolymer concrete to rest and cure for 24 hours.

[0250] Demolding was carried out immediately after curing. Each plate was removed from the frame and the molded geopolymer concrete parts were demolded. The plates were then held under tap water to remove the loosely held particles. Strongly attached mortar particles were removed with a soft brush, if there is any. After all visible mortar particles were removed, the plates were wiped with a wet cloth followed by wiping with a dry cloth. This would make the plates ready for the next cycle. The plates were put back into the frame to repeat the above steps for a total of 10 cycles for Example 7. The plates were stuck at the same position in every cycle.

Comparative Example 1

[0251] The same steel plates and frame before coating as in Example 3 were used to form the mold. The steel plates were sanded to remove any stain, oil, oxides and other residue on the surface and cleaned with ethanol.

[0252] Mineral oil was uniformly brushed on the surface of the steel plates as demolding agent. According to the procedure in Example 6, the OPC concrete was cured and demolded except that mineral oil was coated on the substrate instead of multiple resin-based layers comprising primer and demolding layer. Care was taken to avoid pulling off oil from the mold, which leads to poor concrete surface.

Comparative Example 2

[0253] The same procedure as in Comparative Example 1 was used except that the geopolymer prepared according to Example 5 was cured and demolded by using mineral oil as the demolding agent.

Example 8. Image Analysis of Concrete Surface

[0254] The surface of cured concrete parts was firstly pressed gently with fingers to ensure that all hidden voids or bubbles on the surface were exposed. Then the images of surface of the concrete parts obtained in each cycle were taken and analyzed.

[0255] ImageJ software was used to visualize the distribution of air voids and to quantify the percentage of air voids area on the concrete surface as follows:

[0256] 1. Drag and open the image to be analyzed into ImageJ software;

[0257] 2. Select predetermined area to be analyze, crop it out, and set appropriate scale (e.g. 125×125 mm);

[0258] 3. Adjust brightness and contrast of the image until only air voids are seen, then click “apply”;

[0259] 4. Adjust the threshold to such a value that all air voids can be observed, then click “apply”;

[0260] 5. Use the analyze tab to analyze the air voids, obtain the output of air voids area distribution, percentage of total air voids area based on total area of concrete surface and count of air voids.

[0261] The calculated percentage of air voids area by image analysis of Example 6A-6C, Example 7 and Comparative Example 1-2 were summarized in Table 6.

TABLE-US-00006 TABLE 6 Percentage of air voids area (%) Example Comparative Comparative Cycle 6A 6B 6C 7 Example 1 Example 2 Average (%) 0.42 0.33 0.33 0.29 0.92 1.05 1 0.36 0.38 0.40 0.45 0.59 1.03 2 0.29 0.45 0.31 0.72 0.51 2.16 3 0.20 0.45 0.28 0.62 0.81 1.22 4 0.35 0.25 0.31 0.43 0.54 0.56 5 0.37 0.35 0.36 0.11 1.28 0.68 6 0.51 0.40 0.23 0.18 0.98 0.86 7 0.41 0.49 0.40 0.21 0.90 1.33 8 0.44 0.55 0.48 0.08 0.75 1.09 9 0.31 0.40 0.39 0.05 0.65 1.13 10 0.52 0.38 0.37 0.01 1.74 0.43 11 0.78 0.55 0.40 — 1.78 — 12 0.40 0.26 0.30 — 0.95 — 13 0.29 0.25 0.32 — 0.96 — 14 0.22 0.25 0.26 — 0.97 — 15 0.27 0.46 0.31 — 0.57 — 16 0.54 0.30 0.31 — 0.88 — 17 0.52 0.25 0.32 — 0.76 — 18 0.63 0.36 0.37 — 1.42 — 19 0.36 0.26 0.37 — 0.67 — 20 0.27 0.25 0.29 — 0.95 — 21 0.40 0.30 0.32 — 0.44 — 22 0.34 0.19 0.34 — 0.99 — 23 0.53 0.26 0.40 — 1.18 — 24 0.47 0.24 0.17 — 0.63 — 25 0.60 0.26 0.27 — 1.26 — 26 0.32 0.20 0.48 — 0.62 — 27 0.62 0.33 0.17 — 0.56 — 28 0.53 0.33 0.26 — 0.74 — 29 0.24 0.21 0.25 — 0.98 — 30 0.36 0.17 0.31 — 0.66 — 31 — 0.57 — — 1.11 — 32 — 0.12 — — 0.82 — 33 — 0.43 — — 1.72 — 34 — 0.44 — — 1.09 — 35 — 0.29 — — 1.72 — 36 — 0.39 — — 1.02 — 37 — 0.36 — — 0.52 — 38 — 0.28 — — 0.69 — 39 — 0.18 — — 0.99 — 40 — 0.28 — — 0.68 — 41 — 0.39 — — 0.66 — 42 — 0.23 — — 0.71 — 43 — 0.18 — — 0.71 — 44 — 0.56 — — 0.73 — 45 — 0.33 — — 1.19 — 46 — 0.36 — — 0.88 — 47 — 0.36 — — 1.19 — 48 — 0.20 — — 0.88 — 49 — 0.42 — — 1.40 — 50 — 0.36 — — 0.81 —

[0262] It's shown in Table 6 that the result of concrete surface according to Example 6A-6C, Example 7 have small air voids area percentage throughout the cycles, which is much lower than that of Comparative Example 1-2 in each corresponding cycle.

[0263] FIG. 2 shows the image of the molded OPC concrete surface obtained according to Comparative Example 1 and FIG. 3 shows the image of the molded OPC concrete surface obtained according to Example 6B after 10′.sup.h cycle. It is obvious that many air voids can be found on the surface of Comparative Example 1 while molded concrete in Example 6B has a better surface finish with fewer and smaller air voids on concrete surface.

[0264] Similarly, FIG. 4 shows the image of the molded geopolymer concrete surface obtained according to Comparative Example 2 and FIG. 5 shows the image of the molded geopolymer concrete surface obtained according to Example 7 after 10.sup.th cycle. It is obvious that many air voids can be found on the surface of Comparative Example 2 while molded concrete in Example 7 has a better surface finish with fewer and smaller air voids on concrete surface. Very few residuals of geopolymer concrete was left on the mold after each cycle. The mold didn't need additional maintenance or cleaning process after each cycle. In comparison, cleaning mold in Comparative Example 2 was more difficult than mold in Example 7. Geopolymer mortar was strongly attached to mold surface and had to be scraped out.

[0265] The above results demonstrate that the concrete parts obtained according to the invention have better surface finish than Comparative Examples throughout the cycles even though the application method, person of application and all other variables are held constant. The results also prove that the multiple resin-based layers comprising of primer and demolding layer can adhere strongly to the substrate and produces satisfactory results after 10, 30 or even 50 cycles.

[0266] It is advantageous that the concrete parts obtained according to the invention have lower value of percentage of air voids area and hence smooth surface com-pared with that of Comparative Examples when mineral oil is used as the demolding agent. The above results indicate that the method of the invention successfully produce concrete parts with improved surface finish without preparing the mold in each cycle. The results also showed that the mold according to the present invention can be used for multiple cycles and can be used to product concrete parts with improved surface finish, even after multiple cycles.

Comparative Example 3

[0267] Demolding agent obtained according to Example 2 was brushed on the steel plates to form a demolding layer of 0.2 mm without primer. According to the procedure in Example 6, the OPC concrete was cured and demolded with the exception that the plates without primer thus obtained were used.

[0268] After 3-5 cycles, it was discovered that the demolding layer was partially peeled off from the substrate and the OPC concrete surface obtained after 3-5 cycles no longer had smooth surface desired by the inventors. Therefore, it is essential to have primer between the substrate and the demolding layer to guarantee a consistent and durable performance of the mold coated with multiple resin-based layers according to the invention.

Example 9

[0269] The OPC concrete parts were cured and demolded by the same process according to Example 6B except that the demolding layer was cured in a two-stage process: (1) put the plates into an oven at 23° C. for 2 hours; then (2) put the plates into an oven at 70° C. for 2 hours.

[0270] Average percentage of air voids area of concrete surface obtained according to Example 9 for 10 cycles is 0.09%, showing a satisfactory smooth surface.

Example 10

[0271] The concrete parts were cured and demolded by the same process according to Example 6B except that plates made of steel, aluminum, plywood and PVC resin are individually used as plates of the mold. The pull-off adhesion between multiple resin-based layers comprising primer and demolding layer and each substrate was tested and summarized in Table 7.

TABLE-US-00007 TABLE 7 Pull-off adhesion between multiple resin-based layers and substrates in Example 10 Example Example Example Example 10A 10B 10C 10D Plate steel aluminum plywood PVC material Pull-off >2.5 >1.7 >1.4 No value* adhesion (Mpa) Point of between between inside the — failure demolding demolding wood layer and layer and material dolly dolly *the adhesion is too weak to be measured

Example 11

[0272] The OPC concrete parts were cured and demolded by the same process according to Example 6A-B except that the primer and demolding layer were applied and cured at different temperatures. The curing time was summarized in Table 8.

TABLE-US-00008 TABLE 8 Curing time of primer and demolding layer in Example 11 Demolding Demolding Primer layer layer Example 1 Example 2A Example 2B  5° C. (hours) 48 60 60 40° C. (hours) 8.4 3.2 2.4 70° C. (hours) 2 — —

[0273] The structures, materials, compositions, and methods described herein are intended to be representative examples of the invention, and it will be understood that the scope of the invention is not limited by the scope of the examples. Those skilled in the art will recognize that the invention may be practiced with variations on the disclosed structures, materials, compositions, and methods, and such variations are regarded as within the ambit of the invention. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. The mold and the method of preparing molded parts according to the present invention are therefore not limited to concrete or construction materials as described herein. Those skilled in the art will recognize that the invention may be applicable to a demolding process of a similar nature as described in the invention.