WO2009135279A2

WO2009135279A2 - Manufacturing process of fiber-cement composite materials using portland cement reinforced with inorganic fibers chemically modified by organoselanes

Info

Publication number: WO2009135279A2
Application number: PCT/BR2009/000123
Authority: WO
Inventors: Alexandra Ancelmo Piscitelli Mansur; Otávia Luiz DON NASCIMENTO
Original assignee: Biobrasil Consultoria E Representções Ltda; O. Nascimento Engenharia E Consultoria Ltda
Priority date: 2008-05-09
Filing date: 2009-05-07
Publication date: 2009-11-12
Also published as: BRPI0802008A2; WO2009135279A3; BRPI0802008A8

Abstract

An innovative method for manufacturing fiber-reinforced building products based on fiber-cement composites using inorganic fibers, with or without natural or synthetic polymeric fibers as supplementary reinforcing materials is provided. This invention discloses the formulation, the method of manufacturing and the final fiber-cement products using thermo-chemically treated and stabilized inorganic slag glassy fibers from iron blast furnace plants or derived, but not limited to these, with silane coupling agents, additives, and catalyzers, for reinforcing Portland cement composites. The process can be shortly described by the following steps: a) Mixing and agitation of glassy blast furnace slag fibers in an alcoholic aqueous solution until the fibers are well dispersed and suspended in the solution; b) Thermo-chemical treatment with dewaxing agents and hydrophilization process under stirring; c) Thermo- chemical treatment based on organosilanes and oxidants, dispersants and cross- linking agents at 20-500C; d) Cross-linking surface reactions and fibers drying at 80-1500C for 1-4 hours; e) Preparation of a well mixed slurry with treated fibers, cement, aggregates, supplementary materials, additives, and water; f) Composite production by Hatschek process through deposition of the aqueous fiber-cement slurry on a porous fabric belt positioned on a series of support rolls. The slurry is conveyed by the fabric belt over and through a series of rollers to flatten and shape the slurry; g) Moisture is mostly drained off by the application of vacuum to the slurry and product final shape and dimensions are obtained. This invention discloses an original method for modify blast furnace slag fibers or derived, but not limited to these, in order to improve their alkaline resistance to Portland cement matrix with supplementary cementitious materials. This fibers were used in the manufacturing of fiber-cement composites such as flat and corrugated sheets, shingles, panels, and several others fiber-cement commercial products for architectural and construction applications.

Description

"MANUFACTURING PROCESS OF FIBER-CEMENT COMPOSITE MATERIALS USING PORTLAND CEMENT REINFORCED WITH INORGANIC FIBERS CHEMICALLY MODIFIED BY ORGANOSILANES"

An innovative method for manufacturing fiber-reinforced building products based on fiber-cement composites using inorganic fibers of glassy slag, with or without natural or synthetic polymeric fibers as supplementary reinforcing materials is presented. More precisely, this invention discloses a totally original method for fiber-cement composites based on Portland cement reinforced by synthetic inorganic fibers, mostly glassy, as a substitute for asbestos fibers, recycled from sub-products of blast furnace plants chemically treated and stabilized to improve their alkaline resistance to Portland cement matrix to be used in the manufacturing of fiber-cement composites such as flat and corrugated sheets, shingles, panels, and several others fiber-cement commercial products for architectural and construction applications. Composites are engineered materials made from two or more constituent materials, in the case of a fiber-reinforced composite, it is a material made of one or more fibers, immersed in a continuous phase, named matrix. Tenacity and ductility are two important properties when dealing with thin construction assemblies improving handling, during manufacturing, transporting and assembling, and so reducing cracking, or even breaking. Fibers increase deformation and load-bearing capabilities of composite materials, mostly when submitted to tension, flexural and compression tests, and impact loads.

In the manufacturing of construction materials, products based on Portland cement reinforced with inorganic asbestos fibers are, in general, called fiber-cement. Asbestos-cement, popular name of fiber-cement, is a composite material that consists of more than 90% by weight of Portland cement and calcareous filler and less than 10% by weight of chrysotile asbestos fibers developed by an Austrian industrial Ludwig Hatschek at the end of 19^th century (pre-formed asbestos-cement products). Since then, asbestos-cement composites have been widely used in producing shingles, water tanks and roofing accessories. Asbestos is a group of fibrous silicate minerals largely used in fiber- cement products such as corrugated sheets and water tanks. The use of asbestos has been limited or banned in many countries what has driven the interest for asbestos-free alternative fibers.

The main goal of this process was the development of an innovative technology for manufacturing corrugated sheets for roofing reinforced with inorganic slag fibers from blast furnace plants chemically treated and resistant to the alkaline media characteristic of cementitious materials, for fiber-cement shingles and other products by Hatschek manufacturing technique, but not limited to one specific product or process.

The international trend in the construction market is the running for new composites technologies. Among the different types of materials used in Portland cement-based composites are steel fiber, nylon fiber, carbon fiber, vegetal fiber and also ceramic fibers and glass fibers. Conventional E-type glass fiber suffer loss of physical properties with time, due to alkali attack from Portland cement matrix, which affects, mostly, its tenacity, reducing the flexibility and leading to embrittlement of the fiber. In the last years, Alkali Resistant (AR) glass fiber was developed by incorporation of about 16% of zirconium oxide in glass matrix (TEZUKA, 1989; PARDELA e AGUILA, 1998) to overcome the poor durability of conventional glass fiber in alkaline media. The costs associated with AR fiber are extremely high, about three to five times more expensive than conventional glass fibers, largely limiting their use in popular houses and by low income population. On the other hand, Brazilian construction, in habitation, industrial and agricultural fields, demands low-cost technologies, with rational use of labor work and reducing material losses. It is also identified the global trend for using fiber reinforced materials in construction due to the possibility of manufacturing slender components, besides the high capability for energy absorption of dynamic loads, being very interesting from an economical aspect the viability of alternative fibers in Portland cement systems. In order to reach that goal, it is necessary to protect fiber from chemical attack of strong alkaline media characteristic from Portland cement. Usually this is obtained by using latex modifiers, silica fume or even fiber surface treatment.

Discarded solids residues as raw material for fiber manufacturing are a renewable source and reduce environmental impacts of landfill. In developed countries, and also in the underdeveloped ones, fibers produced from natural and synthetic residues have been used as recycled materials. Research interest is driven by several aspects such as immobilization of residues in composites and reinforcing of brittle cement matrix, at relatively low cost, availability from discarded residues of industries, use of fibers considered by- products, reduction in energy consumption and of environmental impacts. This chemically modified fibers reinforced composites can be made on a Hatschek machine, with none or minimal modifications.

The concept of using fibers as construction materials reinforcement is not new. Fibers have been used as reinforcement since ancient times, with evidence of the use of asbestos in clay posts manufactured 5,000 years ago. Others applications are associated with animal hair reinforcing wall mortars and Egyptians' mud-bricks made with baked clay reinforced with straw. However, the addition of fibers in concrete is a relatively new technology. The use of discontinuous fibers in concrete matrix began in the early 1960s, when steel fibers, mineral fibers and glass fibers came to the market. In Brazil, alternative fibers choices, like synthetic polymeric ones, such as poly(vinyl alcohol) (PVA) and polypropylene (PP), glass fibers, steel fibers, and also vegetal fibers, such as cocoa, sisal, bamboo and others, were introduced at the end of 70's, with some systematic studies, where their potential use in cement reinforcement was investigated. The use of natural fibers as a reinforcing material was motivated by their low cost, abundance of raw materials, environmental and economical issues, once traditional construction materials have a high cost, caused by the costs related to energy and transportation.

According to their chemical composition, fibers are classified as organic and inorganic. They can be further categorized into natural and synthetic. There are in the world reported literature controversies involving some types of fibers and their classification, mostly concerning vegetal or cellulosic fibers and animal fibers such as solids residues of leather processing industries, tanned leather waste, animal hair, etc. Controversy arise despite of being called natural fibers, from animals tissues, they are processed materials that have been submitted to chemical, thermal, and mechanical processes that modified their properties before their use in composites. In this text, to avoid mistakes, inorganic natural fibers are those that were not man-made through industrial processing, as fibers or agglomerates, like chrysotile asbestos. On the other hand, inorganic synthetic or artificial fiber is the man made through one or more chemical, physical or both (physical-chemical) process modifying natural materials, for example, glass fiber, ceramic fiber, slag fiber, where the last one is the specific subject of this work.

Slag fibers are inorganic based on their chemical composition mostly composed by metallic oxides, like silicon oxide (silica, SiO₂), calcium oxide (calcia, CaO), aluminum (alumina, AI₂O₃), magnesium oxide (magnesia, MgO), iron oxide (Fe₂Os), sodium oxide (Na₂O), and potassium oxide (K₂O), among others. Fibers physical dimensions vary in a broad range, mostly from 1.0-20mm in length and l-50μm in diameter, with densities ranging from 2.0 to 2.8 g/cm³ (2.0-2.8 t/m³). Depending on processing conditions from industrial slag cooling, the fibers could be also grouped in stacks or agglomerates twisted in a bunch of fibers. The industrial use of fiber-cement reinforced with glassy inorganic fibers, like glass and slag fibers, is usually limited by their degradation in the alkaline media characteristic of Portland cement. A broad sustainability approach (social-economic-environmental) and the search for continuous improvement of manufacturing process with a global scale competitivity has been promoting the use of by-products of steelmakers industries, mostly those used for clinquer substitution in cement industry and related companies, but they have limited utility because of their high reactivity or low stability. However, yet, no national or global patent have succeed using slag or other residue- derived fiber supplied by steel manufacturers and metallurgical industries, iron casting, to be used as a reinforcement material in fiber-cement composites in a Portland cement matrix, addressing medium and long term reliability.

Chemical reagents from the class of organosilanes have been used as surface modifier agents in all areas of science. It is important to point out that the scientific and technological control of the process joined to adequate selection of system may promote significant changes on the fiber surface by specific chemical functionalities, for instance amine, thiol (synonym of mercaptan or sulfidryl), isocyanate, esters, ether, epoxy, vinyl and others, besides the large possibilities of combining two or more of this groups simultaneously. Therefore, that comes countless possibilities of producing novel chemically modified systems designed for specific application. The chemical features of these moieties, like hydrophilicity, hydrophobicity, acid character, would suit as potential sites for interactions and chemical reactions. In this work, for the first time, it was pioneering used slag fibers from steel manufactures and metallurgical industries where surfaces were chemically modified aiming to improve their alkaline resistance, to be used as reinforcement material in the fiber-cement manufacturing and building materials. In a broad perspective, the final properties of the composites are strong dependent on the individual characteristic of each and every component and also, by the manufacturing process. The theory of cementitious material reinforced by fibers is extensive, were some features of fibers are very important, as shown:

- Type of fibers; - Fiber application;

- Fiber distribution and morphology; - Shape and geometry of fibers;

- Bond strength between fiber-matrix adhesion;

- Volumetric fraction of fibers;

- Intrinsic properties of the fiber; - Fiber surface;

- Cement-fiber mixture process;

- Composites curing method;

- Dimensional stability;

- Chemical stability of dispersed fiber in the composite matrix;

Among several processes of fiber-cement production under commercial scale, Hatschek process comes out as an interesting alternative. It was developed in the 1900's by a researcher with the same name which is still broadly used till now. Basically, this process uses aqueous slurries, where adequate dispersion of fibers in the cementitious matrix is reached. Then, the mixture is drained for water excess removal, forming several layers, typically ranging from 1 to 10mm thick.

The Hatschek process of manufacturing fiber-cement composites based on Portland cement and fibers can be divided in the following steps:

- Fiber dispersion in the aqueous medium making a low viscous and homogeneous suspension;

- Addition of cement with or without fillers, for instance calcareous materials and carbonate salts; - Homogenization of the mixture for fiber dispersion producing the slurry;

- Water excess removal via porous cloth drainage forming uniform layer; - Extrusion by rolling cylinders for producing a sequence of layers, 1-10 mm thick.

- Mold pressing for product shaping (i.e. corrugated sheet, plan sheet);

- Thermal treatment for accelerated curing in other to reach final chemical and mechanical stability of the product.

The substitution of asbestos fibers and polymeric fibers by natural fibers usually, vegetal fibers, has been the choice in many countries, where several patents have been claimed. In the United States, in the patent database search, the following patents were found, dealing with cellulosic base fibers as reinforcing fiber-cement composites: (US 6,942,726) (US 6,872,246) (US 6,811,879) (US 6,676,745) (US 6,676,744) (US 6,572,697) (US 6,138,430) (US 5,785,419) (US 5,641,584) (US 4,985,119). Also in Brazil, several patents were deposited in INPI (Patent Office Brazil) in the last few years, concerning cellulosic based fibers ((PI0313982-4),(PI0104440-0), (PIO 109283 -9), (PI9503532-0), (PI9507048-6), (PI8503236-0), (PI0508132-7)). More specifically, regarding to the chemical modification of natural and synthetic inorganic fibers, the large majority of patents are related to fiber glass products (E-glass, AR-glass, A-glass, S-glass and ECR-glass), natural mineral fibers (wollastonite), using protective layers against high alkalinity, usually from styrene resin or oxides (zirconia, ZrO₂), for instance (US 4118239), (US 4118239), (US 6582511), (US 7354876), (US 4652535), (US 4105492), (US 4910076) (US 4454285). However, no deposit or occurrence has been found in national (Brazilian) or global patent databases, using inorganic fibers or solid residues from metallurgical industries, specifically from slag with chemical modified surfaces, prepared by a reaction of organosilanes, and other reagents, producing a alkali resistant fibers to be potentially used as a reinforcement material in Portland cement matrices.

Before the present invention, the big challenge from technological, economical and commercial perspectives has never been solved concerning to the development of an alternative fiber suitable to replace asbestos that would meet all standards and similar properties with a competitive market price. The fiber should be chemically stable to resist the high alkaline cementitious matrix, dimensionally and mechanically suitable for fiber-cement, viable in an industrial scale to cpmpete in equivalent conditions with other technologies already known. It is well known for decades that natural vegetal fibers mainly those cellulosic fibers from eucalyptus, pine, and other vegetables have undoubtly presented degradation in their structure when submitted to the alkaline matrix in the medium and long term periods. Hence, they have significantly reduced mechanical properties and therefore have caused catastrophic reduction as a choice on structural materials application. However, alternatives for inorganic asbestos fibers have been sought in many countries, such as glass fibers (AR- glass) and synthetic polymeric fibers, mainly polypropylene and PVA. Though, as previously said, the high costs associated with these fibers, prevent their spreading in countries like Brazil and others with large habitation demands for low income population. Other research approach has been developing cementitious matrices with low content of Portland cement and use of pozzolanic materials in other to reduce matrix alkalinity resulting from hydration of calcium phases like Portlandite or Ca(OH)₂, reducing the attack to natural, animal or vegetal, fibers. In addition, as an alternative to control degradation in alkaline media, some manufactures make a treatment of carbonation of fiber-cement in a CO₂-rich environment after production in order to promote the conversion of Portlandite (Ca(OH)₂ ) into calcium carbonate (CaCO₃), reducing the possibility of degradation. The autoclave curing method for fiber-cement composites also improve long term behavior of fibers in cementitious matrix. Usually autoclaving process consists of temperatures in the range of 150-190⁰C and autogenous pressure of 0.5-1.5 MPa. They are not generally used as a widely acceptable definitive solution because of the high costs associated with energy and time-consuming process required, which has significantly restricted the acceptance and its use for preparing natural fibers in building composites.

The present invention discloses an original process of thermo- chemical treatment of inorganic slag fibers mainly from metallurgical and other steel manufacturers (semi-processed, processed or by-products) with chemical composition based on silicon, calcium, and aluminum oxides and minor amounts of other oxides (ferrite-Fe₂θ₃, rutile-TiO₂, Na₂O, K₂O e SO₃), forming a glassy or semi-crystalline matrix, modified through chemical reactions with organosilanes and additives, resulting in a system highly alkali-resistant. These chemically modified fibers are utilized as mechanical reinforcement material in fiber-cement composites based on Portland cement. Among the several processes available for production of plan and corrugated sheets or panels, via aqueous route, Hatschek process was selected in this invention as an example, but it is not limited to it. The innovative technology developed can be basically described by three major phases: Phase-I: named thermo-chemical treatment of oxidative-dewaxing and fiber expansion; Phase-II, named thermo-chemical treatment of surface modification related to structural crosslinking and alkali- resistant protection; Phase-Ill, called modified manufacture Hatschek process. These three phases are exemplified and detailed as follows:

- As a reference, it is recommended the use of 100 kg of slag fiber. The proportions of reagents, solvents and other products are based on the initial fiber mass.

A) PHASE-I - Thermo-chemical treatment of oxidative-dewaxing and fiber expansion:

- Pre-treatment of inorganic slag fibers, more specifically slag from metallurgical and other steel manufacturers by addition of oxidative reagents in concentration of 0.2%- 10% (related to solution total volume) like hydrogen peroxide (H₂O₂), sodium peroxide (Na₂O₂), potassium peroxide (K₂O₂) and dewaxing agents (surfactants) in concentration of 0.1%-5.0% (related to solution total volume), under moderate stirring and heating at (40+ 20) ⁰C for 5-60 minutes, using a proportion of fiber to oxidative-dewaxing aqueous solution total volume of 5%-50%. After reaction period, proceed with the full drainage of reaction vessel obtaining the pre-treated fibers and move to the next step of thermo-chemical treatment. B) PHASE-II - thermo-chemical treatment of surface modification related to structural crosslinking and alkali-resistant protection:

- Preparation of a solution of water in ethanol in the proportion of 50%-95% of ethanol, adjusting the pH of the alcoholic aqueous solution by adding acetic acid, hydrochloric acid or HNO₃, in the range from pH 4-6.5; add the organosilanes, more specifically amino-derived silanes like APTES (3- aminepropyltriethoxysilane), and thiol-derived silanes, like a MPTMS (3- mercaptanpropyltrimethoxysilane) in the fraction of 0.1%-20.0% (volume %) relative to total solution volume (ethanol + water). This chemical reaction process named pre-hydrolysis of alkoxides should be conducted under constant moderate stirring and with heating at 20-40⁰C for a minimum period of 5 and less than 60 minutes.

- In the sequence, prepare a mixture of slag fibers pre-cleaned in previous phase (thermo-chemical treatment of oxidative-dewaxing), using ethanol-water solution with pre-hydrolyzed organosilanes (APTS and MPTMS)₅ in the proportion fiber/solution ratio of l%-30% (% mass), forming a homogeneous stable suspension under moderate stirring; This reaction process should be conducted under moderate stirring, constant, and with heating 20- 5O⁰C for minimum 5 and less than 180 minutes; After half at the time has passed, PVA should be added following the concentration of 0.1%- 1.0% (% mass to slag fiber) and crosslinking reagent usually aldehyde or similar, for instance glutaraldehyde in the proportion of 0.1%- 1% (% mass to slag fiber). These additions would stabilize the organosilanes modifiers and the chemical crosslinking at the surface, through Si-OH, Si-O-Ca, -Si-O-Ca-OH- bonds. Also, crosslinking bonds among fibers are likely to occur. Peroxides (dicumyl and benzoyl) initiators are used as PVA activator reagents in the proportion of 0.1%- 0.5% related to the mass to slag fibers, associated with the presence of acetate and hydroxyl groups.

- Drainage of the liquid phase from the reaction vessel. The treated fibers should be submitted to the final stage of drying and crosslinking through heating at 80-150⁰C for 1-4 hours.

The fibers after this thermo-chemical treatment and drying are stabilized and should proceed to the PHASE-III in the Hatschek process. C) PHASE-III - modified manufacture Hatschek process.

1- Preparation of a fiber suspension which were previously chemically modified and stabilized in Phase I and II in an aqueous solution, in the range of 5-30% related to the total volume of the liquid;

2 - Addition of Portland cement, aggregates (sand, carbonates salts as CaCO₃, MgCO₃ and others), forming a homogeneous and dispersed slurry under agitation with fiber content from 1%-15% related to the cement weight; It may be used other organic fibers, natural or synthetic ones, inorganic fibers, added to the suspension in order to improve the mechanical properties of the final manufactured products;

3 — Introduction to the prepared slurry in the Hatschek process using a moving porous fabric belts pulled by rotating cylinders;

4 — Drying operation by vacuum suction for water excess removal;

5 - Extrusion by cylinders and formation of a multi-layered deposit approximately 1-10 mm thick.

6 - Cut and forming by pressing to reach product final product shape and dimensions.

7 - Submit the composite to the accelerated curing station for final product properties.

8 — Product store and preparation for expedition.

These steps of inorganic slag fiber modification are shown in the diagram of FIGURE.1. In this diagram contains a scheme wherein the numbers represent: (1) Sheaf of slag fibers as supplied, without treatment; (2) Image under high magnification illustrating main equivalent oxides detected on the fiber surface, as represented by silanol groups (Si-OH); it should be stressed that interactions among Al-OH and Ca-OH species are also expected to have occurred on the surface; (3) Schematic generic representation of organosilanes modifiers reacting with water molecules, the "R" being the silane chemical functionality, as example, amine, thiol, and others; (4) Products of organosilanes hydrolysis that will react with fiber surface (silanol, siloxanes, oligomers); (5) Representative drawing of the structure of slag fiber chemically modified for amine groups (NH₂), APTES (3-aminopropyltrietoxysilane).

The diagram that represents the Hatschek manufacturing process is shown in FIGURE.2 adapted from COUTTS, 1992. In this figure, there is an schema wherein the numbers represent: (1) mixer, agitator; (2) cylinder; (3) moving belt; (4) direction of belt rotation; (5) vacuum system; (6) extrusion cylinder indicating direction of rotation; (7) cutting system of sheets; (8) sheet leaving the flattening device. The obtained products after manufacturing process of corrugated sheets resemble the molds used in the pressing of conformation. In FIGURE.3, it is showed a small sample of the diversity of shapes of products that could be obtained through this technique, but not limited however to the examples shown.

There are technical specifications for fiber-cement based roofing materials reinforced with asbestos and others according to the current Brazilian standards (ABNT). Besides that, technical specifications of composites reinforced with by natural vegetal fibers must comply with current Brazilian standards. However, there is no regulation or standard specific for fiber-cement composites reinforced by inorganic fibers, such as mineral or synthetic slag fibers. In that sense, aiming to qualify and at the same time validate the results with similar technologies, until this new regulation been issued by Brazilian agency, the raw materials and the fiber-cement products developed and manufactured under the present original and innovative process were evaluated and certified according to the following standards, regarding to properties, performance, and durability:

NBR 9778/1987 - Hardened mortar and concrete - Determination of water absorption by immersion - porosity and density adapted for fiber characteristics;

• NBR 13998/1997 - Determination of amount of dry mass - Method by oven drying;

NBR 14590/2000 - Determination of resistance to sodium hydroxide solutions;

• NBR 15210-1 - Non-asbestos fiber-cement corrugated sheet and accessories — Part 1 : Classification and requisites;

• NBR 15210-2 - Non-asbestos fiber-cement corrugated sheet and accessories - Part 2: Tests;

• NBR 7581 — Fiber-cement corrugated sheets — Specifications;

One should emphasize that some of these Standards and procedures have to be properly adapted in order to suit for the innovation proposed in this work, because they are not readily applicable to all sort of fiber-cement based composites.

Examples and Comparative Examples

Now, the present invention, will detail some practical examples and comparing with other. However, the present invention is not restricted by these examples.

Several types of slag from metallurgical and other steel manufactures have been used as raw material, all of them supplied as fibers. In other to simplify the text, the following practical results will be related to a single type of slag fiber, that will be referred from now on as slag fiber (FE).

These fibers will always be compared to the inorganic fibers used as reference, made of asbestos chrysotile. At this point, it is important to emphasizing that the example is not a limiting condition or a restriction to the application of the developed technology in this invention for inorganic fibers, such as glass fibers, natural mineral fibers or synthetic (wollastonite and zeolite), but just a simplified way of presenting a model to illustrate and verify the results shown. The description of the manufacturing process of fiber-cement composites was divided in two major sections in order to turn it easier to understand the products that were made. The first step reports the preparation and treatment of slag fiber; the second one describes the Hatschek process to produce fiber-cement corrugated sheets reinforced with slag fibers modified in the current invention. Fiber-cement composites were made using either slag fibers directly from the industry without any modification or those with surfaces modified by this invention in order to compare the main improvements regarding to their properties. Besides that, these two groups (unmodified and modified fibers) were used to produce fiber-cement composites and comparing with composites made utilizing asbestos chrysotile fibers referred as FA. Thus, based on this study, it was possible to evaluate the differences achieved by the innovation and the new technology associated with the modification of the fibers. The characteristics of fibers before the chemical treatment (unmodified) will be described as follows:

Dimensional analysis: length and mean diameter (thickness) of fibers were carried out by optical microscopy image and scanning electron microscopy. The dimensional values were obtained by image processing programs.

The results are summarized in Table 1. Table 1 -Dimensional analysis of evaluated samples. Fiber Type Diameter (e) Length (1)

FE (1-15 ) μm (1,0 -15,0) mm

FA < 10 μm (1,0 a 10,0) mm

The slag fibers (FE) evaluated have presented dimensions in the similar range of that observed for asbestos chrysotile fibers (FA) used as reference in fiber-cement manufacturing. However, it should be noted that asbestos fibers have diameter distribution centered on l-2μm while slag fibers diameters are distributed between 1-15μm.

Water absorption: Method for evaluation: ABNT NBR 9778/1987 - Hardened mortar and concrete — Determination of water absorption by immersion — porosity and density adapted for fiber characteristics. One should emphasize that these standards have to be adapted in order to suit for adequate fiber evaluation. The saturation process was conducted by immersion in water for 72 hours (environmental temperature).

The results obtained from water absorption experiments are shown in Table 2. Slag fibers (FE) as supplied without surface chemical treatment have presented water absorption values quite similar or closer to the obtained for asbestos chrysotile fibers used as reference used as reference in fiber-cement manufacturing. Table 2 - Water absorption measurements for evaluated samples.

Water Absorption Fiber type

(Abs)

FE (as supplied) (40 ± 20)%

FA (asbestos) (50 ± 20)%

Resistance to sodium hydroxide solutions: Method of evaluation: NBR 14590/2000 (cellulosic pulp). The obtained results for the resistance to sodium hydroxide solutions are shown in Table 3.

Table 3 - Results of fiber resistance to sodium hydroxide solutions.

Resistance to 10% Resistance to 18%

Type of fiber sodium hydroxide sodium hydroxide solution (Rio) solution (Rχ₈)

FE (as supplied) (70 +10) % (30 ± 10) %

FA (asbestos) (>99) % (95 ± 2) %

Inorganic slag fibers (FE) without treatment, evaluated according to ABNT standard have presented resistance to sodium hydroxide solutions (Rio e

Ris) lower than that measured for asbestos fibers, mostly for R₁₈ values which demonstrates significant decrease of stability in this alkaline medium. It should be noted that the obtained values are not comparable directly once the selected methodology was developed for cellulosic fibers and derivates and there is a step that involves washing with glacial acetic acid solutions which results in an overestimation of the mass loss. In other words, the actual values are higher than those shown in Table 3.

Morphological analysis through scanning electron microscopy (Jeol, JSM 6360LV Noran) assisted on the investigation of dispersion, shape and distribution of slag fibers, as well the evaluation of their stability behavior after alkaline attack. FIGURE.4 shows the photomicrograph obtained from slag fiber (FE) produced from iron blast furnace slag. FIGURE 5 shows the image obtained from inorganic chrysotile asbestos fibers used as reference (FA). The photomicrographs obtained from slag fiber "as supplied" and after the chemical treatment are shown in FIGURE 6A and FIGURE 6B, respectively. Slag fibers with or without chemical treatment have presented morphology quite similar to the observed from asbestos fibers (rounded). Besides that, they have shown average diameter and length in the same range of chrysotile asbestos fibers. In addition to that, dimensional changes were not identified for slag fibers when comparing fibers before and after thermal treatment, with no evidences of cracks, porosities or failures as a consequence of the surface modification treatment.

The features and properties of inorganic slag fibers after chemical treatment (treated) are described in the following sections:

Water absorption: Method for evaluation: ABNT NBR 9778/1987 -

Hardened mortar and concrete - Determination of water absorption by immersion - porosity and density adapted for fiber characteristics. One should emphasize that the current conventional standards have to be adapted in order to suit for fiber evaluation. The saturation process was conducted by immersion in water for 72 hours (environmental temperature).

The results obtained from water absorption experiments are shown in Table 4.

Table 4 — Water absorption measurements for evaluated samples — Changes in water absorption values before and after the modifier chemical treatment in comparison to reference chrysotile asbestos fiber (FA).

It was observed a satisfactory behavior for both groups of fibers, slag fibers "as supplied" and chemically treated, compared to reference asbestos fibers concerning to water absorption results. It was clearly identified a reduction of water absorption values for treated slag fibers (FE), which is an important evidence of the chemical modification on the inorganic fiber surface in order to reduce its hydration and, as a consequence, minimizing its degradation in alkaline media. Nevertheless, the obtained results are still fully adequate for fiber-cement manufacturing through Hatschek process that utilizes large amount of water, attributing the hybrid behavior to the fibers, partially hydrophilic and hydrophobic. Slag fibers before thermo-chemical treatment (FE as supplied) have presented lower resistance to sodium hydroxide solutions attack than those results from chrysotile asbestos fibers as shown in Table 5. Following the test method of NBR 14590/2000, it can be noted that chemical modification of inorganic slag fibers have promoted a significant increase of resistance to attack and alkaline degradation in both tested parameters Rio and R^ when compared to the unmodified fiber (FE) as supplied. Ri₈ average result is over than 80%, quite higher than as supplied slag fibers (unmodified) e closer to the measured values for reference asbestos fiber (~ 95%). These results has given strong evidence that the present invention has successfully developed and produced an alternative fiber from slag which after being submitted to chemical treatment presented similar behavior to inorganic chrysotile asbestos fibers, concerning to resistance to alkaline degradation. Hence, one should consider the process approved on producing viable fibers to be used as reinforcement material for cementitious matrices and composites production.

In the second stage of evaluation method, the Hatschek process was performed aiming to produce fiber-cement corrugated sheets. Wave type corrugated sheets were produced with thickness typically in the range from 3- 8mm, with variable distance (wave- wave), length of 1.22 m, 2.44 m until 3.66 m, and width from 0.5-1.5 m, as cementitious materials Portland cement of CP- II, CP-III and CPV (CPU E 32,CPIII 40 RS,CP V ARI, CPV ARI-RS, according to ABNT) were tested with and without supplementary cementitious materials and aggregates such as metakaolin, silica fume, silica, sand, and carbonated materials (calcareous powder or calcareous filler). Table 5- Results of resistance to sodium hydroxide solutions for slag fibers as supplied (FE) and after modifying chemical treatment.

Resistance to 10% Resistance to 18%

Type of fiber sodium hydroxide sodium hydroxide solution (Rio) solution (Riβ)

FE (as supplied) (70 ±10) % (30 ± 10) %

FE (treated) (80 + 15) % (80 ± 15) %

FA (asbestos) (>99) % (95 ± 2) %

Slag fibers as supplied and treated slag fibers were used as composite reinforcement material. Typical chemical composition of slag fibers used is shown in Table 6.

Table 6- Typical chemical analysis of slag fibers.

Table 7 shows the usual chemical composition of the supplementary cementitious materials for composites production. These materials are shown as examples of supplementary materials but the choices are not limited to them, and the field of the present invention is not restricted to their use. Several tests for properties evaluation and comparative behavior were conducted with the fiber-cement composites. Therefore, these samples were submitted to many assays of accelerated aging in order to evaluate the physical and chemical stability in the alkaline media of fiber-cement composite matrix.

Table 7 — Chemical analysis of supplementary cementitious materials.

After the accelerated aging assays, morphological and spectroscopic studies were carried out to verify the effect of the chemical modification of slag fiber surface. Scanning electron microscopy technique was used to support the observation and analyze the fiber-cement composites produced with slag fibers before and after the modifier chemical treatment developed for the reinforcement material, in order to assess fibers performance in the alkaline medium found in Portland cement materials.

The microscopy analyses were conducted at magnifications from 5OX-IO₅OOOX for evaluation of the overall behavior, for instance, fiber-matrix bonding and integration, and also the eventual degradation of slag fibers samples as a consequence of cementitious matrix. FIGURE 7 shows the photomicrograph obtained from slag fibers chemically modified by the innovative method developed in this work into the cementitious fiber-cement composite matrix after 28 days of composite manufacturing in the proportion of 4.0% by mass in a matrix of Portland cement type CP-II (specifically, CP-II-E- 42). This image has shown unquestionable evidences of physical and chemical stability of modified fibers in the high alkaline media of fiber-cement composite matrix, once the fibers did not present reduction of original diameter, similar cross-section and hydration features, and the main characteristic brittle and glassy rupture of slag fibers have been clearly maintained.

Other examples can be seen from the scanning electron microscopy images of FIGURE 8A and FIGURE 8B, that have shown wave-corrugated sheets produced with 6% by mass of treated slag fibers and Portland cement type CP-V ARI after 28 days of fiber-cement production indicating absence of hydration of modified fibers. It is also observed a brittle fracture surface of composite characteristic of reduced hydration/integration at the slag fiber- cement matrix interface. On the contrary, slag fibers without chemical treatment for surface modification were completely degradated and incorporated into the Portland cement matrix through hydration process resulting in the formation calcium silicate hydrate phases (C-S-H)₅ as suggested in FIGURE 9A (magnification 250X) and FIGURE 9B (matrix with magnification of 50X). Therefore, inorganic fibers from residues of steel manufacturers and metallurgical industries that have been chemically treated following the novel approach of this invention have kept their physical and chemical stability under the alkaline conditions of Portland cement, endorsing their potential use in the manufacturing process of fiber-cement composites building materials.

FTIR spectra were obtained from slag fibers as supplied (control- without treatment) and chemically treated to verify the presence of the modifier agent at the fiber surface. FTIR analyses of the several chemical groups present onto the fiber surface, samples of fibers before and after treatment were submitted to the spectroscopy method using the diffuse reflectance accessory (DRIFT) and KBr as dispersing agent (20:1, KBr: fibers) without fibers grinding. In FIGURE 10 it is shown the spectral differences between treated (trace 1) and untreated samples (trace 2), with the bands in the wavenumber ranging from 3000-3400 cm^"1 and 1600-1650 cm^"1 which are associated with deformations modes of the amino groups and derivates. In FIGURE 11, the results are presented regarding to the behavior of: slag fibers "as supplied" before mixing with cementitious materials (Cl); after using as a reinforcement material in a cement matrix (C3); and the chemically modified slag after using as a reinforcement material in a cement matrix (C2). It was clearly verified the reduction of the hydration process generally indicated by the presence of a typical band around 960-970 cm^"1. Therefore, the higher alkaline resistance slag fiber chemically modified is mainly associated with the surface hydration reactions.

Ultimately, the product developed in this invention have presented similar mechanical properties when comparing the novel fiber-cement composites produced with total replacement of chrysotile asbestos fiber for chemically treated and modified slag fiber. FIGURE 12 has shown the flexural strength results obtained from wave corrugated sheets conventional product, with 6% (% mass) of asbestos fibers (FA), in comparison to the product developed and produced following this invention, with chemically modified slag fibers (FE). Once again, it should be emphasized that the results presented in this example are not limited to slag fibers, but they could be achieved by using the process presented in the invention, which would be suitable to almost inorganic fibers with chemical composition of metallic oxides similar to slag, as a reinforcement agent in several types of products based on cementitious materials for building construction industry.

Claims

1. A method for providing fiber-cement composite materials using Portland cement reinforced with inorganic fibers chemically modified by organosilanes wherein inorganic fibers are slag glassy fibers or derived, but not limited to these, and the treatment comprises a pre-treatment of cleaning in a step of dewaxing using surface active agents at 0.1-5.0 v%, under moderate stirring and heating the solution at temperature of (40 ± 20) ⁰C for 5-60 minutes, followed by surface modification treatment using a silane-based coupling agent, mostly amino and mercaptan functional silanes at concentration ranging from 1% to 20% related to fiber mass, and aldehyde cross-linking agents, oxidants, catalyzers, and protective additives, such as poly(vinyl alcohol) and similar polymers, in a thermo-chemical process (pH = 4 ± 2) with heating at 20-5O⁰C for 5-180 minutes during reaction step and warming at 80-150⁰C for 1-4 hours for cross-linking and drying, wherein the resultant surface modified fiber is highly alkali resistant and stable in a Portland cement matrix. Then, they were incorporated in the ratio of 1-20 wt% related to the total solids content of a slurry for Hatschek precast manufacturing technique to obtain fiber-cement composites products, such as flat sheets, corrugated sheets, shingles, and panels, but not limited to these building products.