The presented paper deals with utilization of raw and treated coir pith as potential component of cementitious composites. The studied material is coir pith originating from a coconut production. Its applicability as cement mixture component was assessed in terms of the physical properties of concrete containing different amount of coir pith. Basic physical properties, compressive and bending strength, and hygric transport characteristics as well as thermal properties belong among the studied characteristics. It was proved that the concrete with 5% (by mass of cement) of this waste material shows appropriate physical properties and it gives rise to an applicable material for building structures. Generally, the coir pith can be regarded as lightening additive. When 10% of coir pith was added, it has led to higher deterioration of properties than what is acceptable since such dosing is greatly increasing the total porosity. The influence of chemical treatment of coir pith was evaluated as well; both tested treatment methods improved the performance of cementitious composites while the acetylation was somewhat more effective the treatment by NaOH.
Concrete is conventionally produced from Portland cement, water, and aggregates but nowadays virtually whole world concrete production applies also other components (additives, admixtures) in order to improve the concrete properties, cut production costs, or reduce environmental impact—that is, energy and natural resources consumption—of concrete production. One of the most widely studied and used groups of concrete additives represents supplementary cementitious materials (SCM). SCM can be used as a partial cement replacement in concrete production [
All mentioned SCM are artificial materials, originating in a manufacturing process. However, as cement replacement can be also used as natural materials, more common are natural minerals such as zeolites [
In this paper, the studied material is agricultural waste originating in a coconut production. Very little attention was paid to this topic and only few papers dealing with this topic were found in common sources. Olanipekun et al. [
The utilization of a coir pith as concrete additive is the matter of this study. Coir piths with three different chemical treatments were used as additive in dosing of 5 and 10% of Portland cement content in concrete mixtures. Its applicability was investigated by means of physical characteristics determination. Among studied properties belong the basic physical characteristic, mechanical strength, hygric transport parameters, and thermal properties. Achieved results were compared with the reference material, concrete with no coir pith added.
Compositions of studied concrete mixtures are presented in Table
Composition of concrete mixtures (kg/m3).
Ref | A-5 | A-10 | B-5 | B-10 | C-5 | C-10 | |
---|---|---|---|---|---|---|---|
Silica sand 0.1/0.6 mm | 500 | 500 | 500 | 500 | 500 | 500 | 500 |
Silica sand 0.3/0.8 mm | 321 | 321 | 321 | 321 | 321 | 321 | 321 |
Silica sand 0.6/1.2 mm | 250 | 250 | 250 | 250 | 250 | 250 | 250 |
Silica sand 1/4 mm | 179 | 179 | 179 | 179 | 179 | 179 | 179 |
Plasticizer SIKA 1035 | 5.4 | 5.4 | 5.4 | 5.4 | 5.4 | 5.4 | 5.4 |
CEM I 52.5 R | 563 | 563 | 563 | 563 | 563 | 563 | 563 |
Coir pith A type | 0 | 26.8 | 53.6 | 0 | 0 | 0 | 0 |
Coir pith B type | 0 | 0 | 0 | 26.8 | 53.6 | 0 | 0 |
Coir pith C type | 0 | 0 | 0 | 0 | 0 | 26.8 | 53.6 |
W/C ratio | 0.52 | 0.52 | 0.52 | 0.52 | 0.52 | 0.52 | 0.52 |
Chemical composition of cement CEM I 52.5 R.
Component | Amount [% by mass] |
---|---|
CaO | 64.9 |
SiO2 | 18.1 |
Al2O3 | 6.4 |
Fe2O3 | 2.4 |
MgO | 1 |
Na2O | 0.3 |
K2O | 1.2 |
SO3 | 4.9 |
P2O5 | 0.2 |
Mineralogical composition of cement CEM I 52.5 R.
Component | Amount [% by mass] |
---|---|
C3S | 66.1 |
C2S | 2.3 |
C3A | 12.9 |
C4AF | 7.3 |
Chemical treatment of coir piths.
Treatment of coir pith | Matrix density [kg m−3] | |
---|---|---|
Coir pith A | Untreated | 1535 |
Coir pith B | Sodium hydroxide treated | 1403 |
Coir pith C | Acetylation treated | 1341 |
Granulometry curves of three types of coir pith.
The measurements of material parameters of hardened concrete specimens were performed after 28 days of standard curing (100% RH). It took place in a conditioned laboratory at the temperature of 22 ± 1°C and 25–30% of relative humidity. List of utilized specimens for particular measurement is presented in Table
List of specimens.
Measurement | Dimension [mm] | Number of samples |
---|---|---|
Water vacuum saturation method | 50 × 50 × 50 | 3 |
Cups methods | ø115 | 3 |
Absorption experiment | 50 × 50 × 50 | 3 |
Thermal properties | 70 × 70 × 70 | 3 |
Porosimetry | 50 × 50 × 50 | 2 |
Mechanical properties | 40 × 40 × 160 | 3 |
Bulk density, matrix density, and open porosity were measured using the water vacuum saturation method [
Characterization of a pore structure was determined by the mercury intrusion porosimetry. This method is based on the determination of the external pressure needed to force the mercury into a pore against the opposing force of the liquid’s surface tension. The pore size is then calculated from the measured pressure using Washburn’s equation. The experiments were carried out using instruments PASCAL 140 and 440 (Thermo Scientific). The range of an applied pressure corresponds to the pore radius from 10 nm to 100
Mechanical properties as compressive strength and bending strength were measured according to standards [
Measurement of water vapour transport parameters was performed applying the cup methods (dry-cup and wet-cup) [
The water liquid transport was characterized by the water absorption coefficient. Specimens were insulated, as in the case of water vapour transport, on four lateral sides. Then, the face side of specimens was immersed 1-2 mm in the water. Constant water level in the tank was achieved by a Mariotte bottle with two capillary tubes. One of them, inside diameter of 2 mm, was ducked under the water level. The second one, inside diameter of 5 mm, was above water level. The automatic balance allowed for recording the increase of mass. The water absorption coefficient was calculated from the sorptivity plot [
Using the device ISOMET 2104 [
Results obtained from the water vacuum saturation method are summarized in Table
Basic physical properties.
Material | Bulk density | Matrix density | Open porosity |
---|---|---|---|
[kg m−3] | [kg m−3] | [%] | |
Ref. | 2072 | 2526 | 18.0 |
A-5 | 1857 | 2307 | 19.5 |
A-10 | 1602 | 2214 | 27.6 |
B-5 | 1846 | 2287 | 19.3 |
B-10 | 1564 | 2178 | 29.0 |
C-5 | 1874 | 2303 | 18.6 |
C-10 | 1588 | 2208 | 28.1 |
Pore size distribution curve.
Compressive strength and bending strength of composites are presented in Table
Mechanical properties.
Material | Compressive strength | Bending strength |
---|---|---|
[MPa] | [MPa] | |
Ref. | 63.1 | 9.8 |
A-5 | 40.1 | 9.3 |
A-10 | 15.2 | 4.3 |
B-5 | 47.6 | 8.5 |
B-10 | 12.8 | 4.1 |
C-5 | 48.3 | 9.5 |
C-10 | 14.5 | 4.5 |
Measured water vapour transport properties are presented in Table
Water vapour transport parameters: dry-cup arrangement.
Material | Water vapour diffusion permeability | Water vapour diffusion coefficient | Water vapour diffusion resistance factor |
---|---|---|---|
[s] | [m2s−1] | [—] | |
Ref. |
|
|
50.9 |
A-5 |
|
|
48.4 |
A-10 |
|
|
24.9 |
B-5 |
|
|
44.5 |
B-10 |
|
|
25.8 |
C-5 |
|
|
45.3 |
C-10 |
|
|
25.6 |
Water vapour transport parameters: wet-cup arrangement.
Material | Water vapour diffusion permeability | Water vapour diffusion coefficient | Water vapour diffusion resistance factor |
---|---|---|---|
[s] | [m2s−1] | [—] | |
Ref. |
|
|
37.1 |
A-5 |
|
|
32.3 |
A-10 |
|
|
9.3 |
B-5 |
|
|
29.0 |
B-10 |
|
|
11.4 |
C-5 |
|
|
29.7 |
C-10 |
|
|
9.6 |
In Table
Liquid water transport parameters.
Material | Water absorption coefficient | Apparent moisture diffusivity |
---|---|---|
[kg m−2s−1/2] | [m2 s−1] | |
Ref. | 0.018 |
|
A-5 | 0.019 |
|
A-10 | 0.193 |
|
B-5 | 0.019 |
|
B-10 | 0.199 |
|
C-5 | 0.020 |
|
C-10 | 0.241 |
|
Coefficient of thermal conductivity
Influence of moisture and coir pith admixture on coefficient of thermal conductivity.
In Figure
Influence of moisture and coir pith additive on specific heat capacity.
The matter of this paper was to determine possibilities of utilization of coir pith as component of cementitious materials. Coir pith is agricultural waste originating in coconut production. Its utilization in concrete production would have both economic and ecologic advantages. The aims of this study were to find out appropriate amount of coir pith dosing and also to determine influence of chemical treatment of the waste material on physical properties of concrete. Studied coir pith had three different forms of chemical treatments: no treatment, sodium hydroxide treatment, and acetylation treatment by help of acetic anhydride. Six concrete mixtures differed in amount of coir pith dosing (5% or 10% of cement content) and in type of used coir pith. Achieved results were compared with the reference material with no coir pith. The influence of utilized coir pith can be summarized as follows: Utilization of 5% coir pith led to bulk density decrease (by about 10%), matrix density decrease (by about 9%), and almost no changes in open porosity. When 10% of this waste material was used, bulk density and matrix density went down more substantially (by about 24%, resp., by 13%), while open porosity decreased by 10%. No considerable influence of chemical treatment on porosity was observed. Mechanical properties were also decreased by utilization of coir pith. Compressive strength of concrete containing 10% of coir pith went down by almost 78%; therefore, utilization of such amount of waste material is not useful. However, utilization of 5% of SCM leads to quite appropriate results. In this case, positive effect of chemical treatment was proved. When chemical treated coir pith was used, values of compressive strength fell down by about 24%. Regarding bending strength, 5% of coir pith led to comparable values like in the case of reference material. When higher percentage of the waste material was used, bending strength decreased by about 56%. Measured hygric properties can be divided into two parts according to physical state of water. Water liquid transport characteristic and water vapour transport characteristic were measured. It was proved that by utilization of 5% of coir pith ability of water transport was comparable with reference concrete. However, when 10% of cement was replaced, water transport ability increases considerably. Thermal properties show high dependency on moisture content. However, regarding the influence of coir pith utilized as cement replacement, it was proved that this waste material improved thermal insulating abilities of final concrete. The higher amount of coir pith material contains the better thermal insulator concrete is.
The experimental results summarized above show that although utilization of coir pith would be positive from the economic as well as environmental point of view, its applicability is limited by final physical properties of concrete. In our study, 5% of coir pith dosage leads to appropriate building material. When 10% of this waste material is used, physical properties are deteriorated more than what is acceptable.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This research has been supported by the Grant Agency of the Czech Technical University in Prague, Grant no. SGS13/165/OHK1/3T/11, by the European Social Fund within the framework of realizing the Project “CZ.1.07/2.3.00/30.0034, Support of Intersectoral Mobility and Quality Enhancement of Research Teams at Czech Technical University in Prague” and by the European Union OP RDI Project “CZ.1.05/2.1.00/03.0091, University Centre for Energy Efficient Buildings.”