WO2012115500A1

WO2012115500A1 - A green engineered cementitious composite

Info

Publication number: WO2012115500A1
Application number: PCT/MY2011/000200
Authority: WO
Inventors: Kabir SHAHID; Mohamed Altwair NURDEEN; Azmi Bin Megat Johari MEGAT
Original assignee: Universiti Sains Malaysia
Priority date: 2011-02-23
Filing date: 2011-09-09
Publication date: 2012-08-30

Abstract

The present invention discloses an engineered cementitious composite comprising a mortar matrix reinforced with polymeric fibres, in which the mortar matrix includes hydraulic cement, ground palm oil fuel ash, fine aggregates, a viscosifying agent and a water-reducing agent. An optimum design is used that involves producing palm oil fuel ash with the desired physical and chemical properties and grain size, along with the optimum mixing proportions that incorporate measures of palm oil fuel ash as a supplementary cementitious material, and polymeric fibres at a preferred fibre volume fraction, thereby reducing the level of cement use without compromising the mechanical and physical properties of the composite. This formulation provides a cost-effective alternative for producing durable concrete structures while promoting sustainable development and material greenness.

Description

A GREEN ENGINEERED CEMENTITIOUS COMPOSITE

FIELD OF INVENTION

The present invention relates to an engineered cementitious composite (ECC). More particularly, the present invention provides a formulation for a green engineered cementitious composition for use in the building and construction industries, and a method for producing thereof; in which the cementitious composition is obtained from an environmentally sustainable agricultural by-product.

BACKGROUND OF THE INVENTION

Efforts for sustainable development and environmental preservation are necessary in order to balance the economic, social and environmental impacts of the ever-growing human population as it continually strains the finite resources available on this planet. Sustainable development encompasses all types of human activities, whether individual or collective, and relies heavily on every industry for success. This includes the construction as well as the design industries, which have significant potential to reduce the negative impacts of their activities on the environment through the development and use of new materials, deliberately designed with sustainability as a primary goal. This can be accomplished through many methods, such as the use of new materials to extend infrastructure service life, the development of improved materials to replace less sustainable materials, or the replacement of dwindling raw materials with suitable waste products.

The cement industry is no exception in the effort for sustainability. Although cement is a very versatile building material, it is made from non-renewable resources. It requires high amounts of energy in the manufacturing process, and it produces high amounts of C0₂, which is one of the main contributors to global warming. The manufacture of one tonne of cement produces 0.5 tonne of chemical CO2, in a reaction that takes place at 1450°C. An additional 0.4 tonne of CO2 is given off as a result of the burning of carbon fuel to provide this heat. In short, the production of 1 tonne of cement results in the release of 1 tonne of C0₂ into the atmosphere. It is estimated that 5% to 8% of global C0₂ emissions come from cement production, which is the second fastest growing source of C0₂ emissions. Without altering the chemistry of cement, the reaction component of this CO₂ can not be changed. Furthermore, cement is one of the raw ingredients that go into the production of concrete, which is also known as the most popular construction material. In general, a typical mortar consists of approximately 45% cement by volume, and approximately 10% to 15% cement by weight for concrete. The demand for concrete is predicted to double in the next decade; this trend is decidedly unsustainable.

In order to overcome the economic and environmental impacts resulting from the use of large amounts of cement, the proportion of "pure" cement in a cement-based mixture can be reduced by replacing some of it with other pozzolanic material, which has the ability to act as a cement-like binder. In the existing technologies, industrial wastes including fly ash, slag and silica fume have the potential of being pozzolana.

Nevertheless, while every tonne of pozzolan effectively saves a tonne of cement, there are often engineering constraints limiting the percentage of pure cement that can be replaced. These cement binders also need to present comparable or better properties and lower costs compared to the existing cement material.

There are a few patented technologies over the prior art relating to the concrete or cementitious compositions. PCT Publication No. WO2009085535 discloses a concrete which is optimized for high workability and high strength to cement ratio. This concrete composition has a 28-day design compressive strength of 4000psi and a slump of approximately 5 inches. It is made up of hydraulic cement, pozzolanic material, fine aggregate, coarse aggregate, water and air-entraining agent. The pozzolanic material used is a Type C fly ash. Another cementitious mixture containing high pozzolan cement replacement and compatibilizing admixture thereof is disclosed in U.S. Patent No. US2002005148. The cementitious mixture disclosed comprises a hydraulic cement with greater than approximately 10% by weight of a pozzolanic cement replacement selected from fly ash, slag, natural pozzolana and mixture thereof. A compatabilizing derivatized polycarboxylate polymer dispersant capable of reducing water in combination with an accelerator are also disclosed in this cementitious composition. It is revealed by the prior art that the fly ash is a pozzolanic material which is popularly used as a cement replacement material in concrete in comparison with other pozzolanic materials. Producers of fly ash contend that it is harmless; nevertheless according to the U.S. Environmental Protection Agency (EPA), fly ash contains heavy metals, including nickel, vanadium, arsenic, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, lead, selenium and radium. Additionally, traces of radioactive materials are also present in fly ash. Given the large quantities of fly ash that are produced, a tremendous amount of radioactive waste is generated. In many parts of the world, a limit has been set on the level of radioactive permitted in building materials made using fly ash. All this indicates that fly ash can pose serious environmental problems to the people who handle this material, as well as to those in the vicinity of infrastructure built with fly ash.

Although more fly ash is used beneficially in the cement and construction industry, more than 65% of fly ash produced from coal power station is still disposed of. As a result, the disposal of fly ash has become a growing concern for many countries worldwide. Furthermore, the hazardous nature of fly ash can create surface and groundwater contamination in landfill areas. This is an indication that although fly ash is considered a good replacement material for cement in the production of concrete, it raises great environmental and health issues. Consequently, the EPA is currently proposing to regulate, for the first time, coal combustion residuals (CC s) under the Resource Conservation and Recovery Act (RCRA) to address the risks from the disposal of CCRs generated from the combustion of coal at electric utilities and independent power producers. Palm oil fuel ash (POFA) is a by-product of the palm oil industry, which is considered as an agro-waste that is produced in enormous quantities in Malaysia and Indonesia, as they are the biggest producers of palm oil and palm products in the world. Taking into consideration the high availability of POFA in the country, and the fact that it is an industrial waste that is usually sent to the landfill without being usefully exploited, research can be focused on employing this material towards sustainable development of the concrete industry. The suitability of POFA in the development of a green ECC can be evaluated by three factors, namely its mechanical properties, chemical properties and environmental sustainability. Since environmental concerns are at a peak, the use of POFA in the making of concrete material has many advantages in promoting material greenness, as it involves the recycling of a waste material obtained from renewable sources. ECC is currently emerging in full-scale structural applications, including composite ECC/steel decks of cable-stayed bridges and precast R/ECC coupling beams of several high-rise buildings. It is therefore imperative to incorporate environmental concern into their development. A plausible solution is to replace a portion of cement in ECC with an industrial by-product, without sacrificing its mechanical properties, in general, and tensile ductility, in particular. Therefore, an optimized formulation for producing an ECC using POFA is desired.

SUMMARY OF INVENTION

The primary object of the present invention is to provide an environmentally sustainable ECC by using POFA as one of its major raw materials. Another object of the present invention is to provide an ECC by replacing the hazardous raw material, such as fly ash, with the environmentally friendly agro-waste, POFA, for overcoming adverse environmental impacts.

Still another object of the present invention is to utilize POFA as a cement binder to reduce the use of cement and thus resulting in lower greenhouse gas emissions caused from the production of cement. Still another object of the present invention is to promote and optimize the use of the agro- waste of POFA in order to create another avenue for commercialization of green technology-based products.

Yet another object of the present invention is to develop a formulation of ECC which is having comparable mechanical properties and tensile ductility.

Further object of the present invention is to provide a method for producing a high performance and durable ECC by using POFA as the green-based pozzolanic material to replace non-environmentally friendly pozzolanic material.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention describes an ECC comprising a mortar matrix reinforced with polymeric fibres, in which the mortar matrix includes hydraulic cement, POFA, fine aggregates, a viscosifying agent and a water-reducing agent. Preferably, the composite has an optimum binder replacement level of palm oil fuel ash and an optimum fibre volume fraction which are determined by a micromechanical design procedure.

One of the preferred embodiments of the present invention discloses that the polymeric fibres are polyvinyl alcohol fibres or high modulus polyethylene fibres. Preferably, the polymeric fibres are used in a fraction of 2% to 3% by volume of the composite, and these polymeric fibres have a length ranging from 10mm to 15mm.

Another preferred embodiment of the present invention discloses that the hydraulic cement and the POFA are present in a weight ratio of 10:1 - 10:3. According to the preferred embodiment, the hydraulic cement is ordinary Portland cement.

Still another preferred embodiment of the present invention discloses that the POFA has a particle size ranging from ΙΟμηι to 20μιη.

It is disclosed in yet another preferred embodiment of the present invention that the fine aggregates are silica sands.

Further embodiment of the present invention is an ECC having a viscosifying agent which can be hydroxypropylmethyl cellulose, and a water-reducing agent which can be melamine sulfate formaldehyde or sodium naphthalene sulfonate formaldehyde.

POFA is normally disposed of in landfills with no economic returns, therefore, the recycling of this agro-waste for use as cement replacement in the ECC poses many benefits. The replacement of fly ash by POFA shows a great advantage of energy conservation as POFA can be produced at approximately 400°C to 700°C; whereas the temperature for producing fly ash is generally 1500°C. In the production of POFA, the waste material from palm oil extraction can be directly used, it is non-hazardous and renewable, unlike the fly ash. Besides, the method for moving fly ash from the flue gases can affect the quality of the fly ash produced, but the collection of POFA is very simple since it remains at the bottom of the furnace. In terms of economic savings, fly ash usually provides little cost break depending on the geographic location. Since the POFA is widely available in this region, and involves a relatively simple production process, hence it can result in higher economical benefits. The present invention is capable of producing an ECC which produces moderate hydration, lower hydration heat, less autogenous shrinkage, increased setting time of the paste and improved permeability. Since a lower amount of cement is required to produce the POFA-based ECC, it is also a cost-effective alternative for making concrete structures, with improved durability. All these goals serve to promote sustainable development through simultaneous enhancement of material greenness and infrastructure durability.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an ECC. More particularly, the present invention provides a formulation for a green engineered cementitious composition for use in the building and construction industries, and a method for producing thereof; in which the cementitious composition is obtained from an environmentally sustainable agricultural by-product.

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim. The present invention discloses an ECC comprising a mortar matrix reinforced with polymeric fibres, in which the mortar matrix includes hydraulic cement, POFA, fine aggregates, a viscosifying agent and a water-reducing agent.

The ECC of the present invention is characterized by its green-based formulation, in which the POFA is introduced as a supplemental cementitious material in the production of this ECC. This green-ECC composition can be optimized through systematic experimental investigation concerning various parameters, such as the optimum temperature needed to produce POFA with suitable physical and chemical properties, the optimum particle size for ground POFA, as well as the optimum replacement ratio for using the POFA as a supplemental cementitious material.

According to one of the preferred embodiments of the present invention, the ECC is essentially composed of a matrix of mortar composition and reinforcing polymeric fibres. The major ingredients used for the mortar matrix includes the hydraulic cement and the POFA. The hydraulic cement used in the present invention is preferably the ordinary Portland cement, which is also known as Type-I Portland cement.

The POFA used is preferably derived from the waste materials of palm oil extraction, which include the palm fruit husk and shell. This agro- waste has been combusted and ground to a desired particle size. The physical and mechanical properties of POFA are quite similar to those of fly ash. Both analyses on its physical and chemical properties indicate that POFA is a highly-reactive pozzolanic material that is rich in silica, grouped between Class C and Class F, as specified by the American Society for Testing and Materials, ASTM C618-92a. The performance of the POFA as pozzolanic material in the ECC of the present invention can be tested in terms of its compressive strength, drying shrinkage, water permeability, alkali-silica reaction and sulphate resistance.

According to the preferred embodiment, a micromechanical design procedure can be applied in the present invention, in which the micromechanical principles are used to tailor the various components of the composite at the microstructural level to achieve the exact material performance required. Accordingly, micromechanical model can be developed in order to relate macroscopic properties to the microstructure of the composite; the effect of matrix mechanical properties on composite properties can be reviewed with regard to conditions of composite pseudo-strain-hardening. A systematic investigation can then be conducted on the effect of matrix composition on matrix properties.

Evaluations are carried out to determine the optimum temperature needed to produce the POFA in order to control the carbon content, and the optimum particle size for the ground POFA. Only matrices with suitable fracture toughness, as defined by the micromechanical model, tend to retain the pseudo-strain-hardening property, while the composite elastic modulus tends to increase for all matrices with fine aggregates.

Therefore, in order to keep the fracture toughness of the matrix low, as well as to prevent large matrix particles from dominating fiber dispersion, the particle size of the ground POFA and the size of the fine aggregate can be controlled to obtain a grain size distribution around 100 μιη to 200 μηι.

This matrix design can be further evaluated to determine the optimum fibre volume fraction. An optimal material composition can be achieved by combining the matrix design with a moderately low fibre volume fraction of less than 2 to 3%. The optimum level at which the POFA can be used to replace the cement binder to satisfy the multiple cracking criteria can be obtained via a series of appropriate experiments. This systematic microstructure tailoring of the green ECC can be carried out in order to develop an optimal design that produces mechanical properties, such as tension, compression, shear, fatigue and creep, and physical properties, including shrinkage, and freeze-thaw durability that satisfy or even exceed standards and specifications for ECC. In accordance with the preferred embodiment of the present invention, the hydraulic cement and the POFA are present in a weight ratio of 10:1 to 10:3. Most preferably, the cement to POFA ratio is 10:2. It is to be noted that an optimal cement to POFA ratio is vital in order to ensure the minimum use of cement to produce the ECC with high quality and performance.

As set forth in the foregoing description, the ECC also contains fine aggregates. It is disclosed in yet another preferred embodiment of the present invention that the fine aggregates are silica sands. The chemical additives applied in the ECC composition include the viscosifying agent and the water-reducing agent which work together to regulate the workability of the composition as well as to achieve the consistent rheological properties for better fibre distribution. Preferably, the viscosifying agent is hydroxypropylmethyl cellulose whereas the water-reducing agent is melamine sulfate formaldehyde or sodium naphthalene sulfonate formaldehyde. In accordance with another preferred embodiment of the present invention, the polymeric fibres used are polyvinyl alcohol fibres or high modulus polyethylene fibres. The preferred polyvinyl alcohol fibres can be used at a moderate volume fraction of 2% to 3%, with the optimal length determined. Preferably, these polymeric fibres have a length ranging from 10mm to 15mm. The fibres are preferably surface- coated with oil to reduce the fibre/matrix interfacial bond strength, which is contributed by the fibre-matrix chemical and friction bonds.

The present invention involves a procedure for producing ECC comprising the steps of producing POFA ash using the optimum temperature to achieve desired physical and chemical properties, grinding of POFA to obtain optimum particle size to maximize pozzolanic properties and the reactivity of POFA and to keep the fracture toughness of the matrix low and preparing the optimum mix composition for the green ECC using the optimum binder replacement level of POFA and the optimum fibre volume fraction. Preferably, testing process for demonstrating composite performance can be conducted. These tests include the fibre dispersion test, flexural test, compressive strength, scanning electron microscope (SEM) test, direct tensile test, deformability and viscosity test. This is followed by the testing process for durability of green ECC concrete which includes the alkali silica reaction test, chloride immersion test, water permeability test and fire-resistance test.

As set forth in the preceding description, the optimal composite mixture for POFA- based ECC is determined by observing the influence of the mixture parameters, including the particle size of the POFA, ratio of the POFA in the mixture, water to binder ratio and length of fibres.

The introduction of ground POFA produces moderate hydration, which is desirable within the conditions of micromechanical design for the production of ECC. It has also demonstrated that the use of POFA can increase the setting time of the paste, which is a property that is required in the production of ECC, due to the mixing time needed in order to disperse the fibres throughout the matrix. Therefore, the present invention also provides further technological knowledge concerning the use of POFA, especially in the engineering of cementitious composites.

The composite's performance can be demonstrated through testing of the mechanical properties of this POFA-based ECC, through techniques such as the SEM, compressive strength test, direct tensile test, deformability and viscosity test, flexural test and fibre dispersion test. Durability of the POFA-based ECC concrete is determined through durability tests, such as alkali-silica reaction test, chloride immersion test and water permeability test.

The micromechanical properties of the green-ECC developed, such as the single fibre pull-out test which studies the relationship between the pull load and the displacement of a fibre when it is pulled out of the matrix, and the matrix fracture toughness test, indicate that the micromechanical properties match the conditions of micromechanical design. The ECC achieves strain-hardening in uniaxial tension, which indicates the comparable tensile ductility, it also satisfies the multiple cracking criteria. Testing of the composite's performance and durability also produces satisfactory results.

The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.

Claims

1. An engineered cementitious composite comprising a mortar matrix reinforced with polymeric fibres, in which the mortar matrix includes hydraulic cement, palm oil fuel ash, fine aggregates, a viscosifying agent and a water-reducing agent.

2. A composite according to claim 1 having an optimum binder replacement level of palm oil fuel ash and an optimum fibre volume fraction determined by a micromechanical design procedure.

3. A composite according to claim 1, wherein the polymeric fibres are polyvinyl alcohol fibres or high modulus polyethylene fibres.

4. A composite according to claim 1 , wherein the polymeric fibres are used in a fraction of 2% to 3% by volume of the composite.

5. A composite according to claim 1, wherein the polymeric fibres have a length ranging from 10mm to 15mm.

6. A composite according to claim 1 , wherein the hydraulic cement and the palm oil fuel ash are present in a weight ratio of 10:1 to 10:3.

7. A composite according to claim 1, wherein the hydraulic cement is ordinary Portland cement.

8. A composite according to claim 1, wherein the palm oil fuel ash has a particle size ranging from ΙΟμηι to 20μιη.

9. A composite according to claim 1 , wherein the fine aggregates are silica sands.

10. A composite according to claim 1, wherein the viscosifying agent is hydroxypropylmethyl cellulose.

11. A composite according to claim 1 , wherein the water-reducing agent is melamine sulfate formaldehyde or sodium naphthalene sulfonate formaldehyde.