Eco-Friendly Concrete Mix Design with Industrial Wastes by Perceptive of Constituents Chemistry

Keywords: Crushed Rock Powder (CRP), Carbon Dioxide Curing (CC), Water Curing (WC), Rice Husk Ash Concrete (RHC), Fly Ash Concrete (FHC), Air Curing (AC).

Introduction

In recent years, remarkable efforts have been taken in the domain of concrete engineering and technology to research and study the utilization of by-products and waste materials in the production of concrete. The successful utilization of these materials will result in the reduction of global warming and environmental loading, waste management cost and concrete production cost, besides enhancing the properties of concrete in both fresh and hardened state. Efforts in this direction have been focused in identifying and optimizing the benefits of different types of cement replacement materials as well as identifying alternative materials as aggregates in concrete and by better perceptive of constituents chemistry of the concrete mix.

Prachoom Khamput¹, studied the compressive strength of concrete using quarry dust as fine aggregate instead of sand. Ratio of cement : sand : rock is 1 : 2 : 4 (by weight) and at water-cement ratio (w/c) of 0.45. The paper published by Raman S. N², reports the experimental study undertaken to investigate some properties of quarry dust and discusses the suitability of those properties to enable quarry dust to be used as partial replacement material for sand in concrete. Ilangovana R³ and Chaturanga Lakshani Kapugamage⁴, studied the feasibility of the usage of Quarry Rock Dust as hundred percent substitutes for Natural Sand in concrete. It is found that the compressive, flexural strength and Durability Studies of concrete made of Quarry Rock Dust are nearly 10% more than the conventional concrete. Alireza Naji Givi⁵, presents an overview of the work carried out on the use of RHA as partial replacement of cement in mortar and concrete. Habeeb G.A⁶. and Muhammad Harunur Rashid⁷, conducted an experimental investigation on the influence of Rice Husk Ash (RHA). Average Particle Size (APS) on the mechanical properties and drying shrinkage of the produced RHA blended concrete. Dao Van Dong⁸, presents several key properties of high strength concrete using rice husk ashes (RHAs). Mauro M. Tashima⁹  and Shao Y¹⁰, evaluates how different contents of rice husk ash (RHA) added to concrete may influence its physical and mechanical properties.

The recent development in the field of concrete technology represents a giant step towards making concrete a high-tech material with enhanced characteristics. Some alternative materials already have been used as a part of natural river sand. For example, Fly ash, slag and lime stone, granite powder were used in concrete mixture as a partial replacement of natural sand. In present work, quarry rock dust is used as a sand replacement material. Crushed Rock Powder (Rock dust/ quarry dust) is a by-product generated from quarrying activities involved in the production of crushed coarse aggregate. When the quarry dust is observed with edges, their size is very close to sand. Thus the quarry dust may be examined the physical properties by using the standard of fine aggregate. Hence Crushed Rock Powder is used as an alternative of natural sand and its effects on the compressive strength of the different levels of CRP concretes were investigated. Felixkala T¹¹ studied the properties of HPC with granite powder as fine aggregate. The test results show clearly that granite powder of marginal quantity as partial sand replacement has beneficial effect on concrete properties.

In Greece, a recent report by Papadakis¹² has revealed that although about 10 million tons of fly ash is generated annually, their absorption in several applications (mainly the cement industry) is stuck at 10%. The amounts that remain unused obviously create acute environmental problems and moreover inhibit the path towards sustainability. For increasing the utilization rate of this by-product, it is necessary to fully explore its dynamic and pozzolanic potential, but also to come up with methods of enhancing its slow reaction. This task however becomes difficult when dealing with a very heterogeneous product, where not all streams are the same, chemically or physically, and furthermore, when the effect of each of those parameters on the hydration of fly ash/cement (FC) systems has not yet been completely understood. Raman¹³, reports the experimental study undertaken to investigate the influence of partial replacement of sand with quarry dust, and cement with fly ash on the concrete compressive strength development. Two types of replacement proportion of sand with quarry dust, 20% and 40% were practiced in the concrete mixes except in the control concrete mix. Besides, replacement proportion of 10% cement content with fly ash was practiced in some of the concrete mixes. Two types of curing methods, water curing and air curing under controlled laboratory conditions were practiced during the entire study. Recorded results indicate that concrete incorporating quarry dust without the inclusion of fly ash exhibited lower compressive strength than the control concrete at all ages. This weakness was overcome by the inclusion of fly ash into the quarry dust concrete in which it resulted in the enhanced compressive strength at almost all conditions. It can be concluded that quarry dust can be utilized as partial replacement material to sand, in the presence of fly ash, to produce concretes with fair ranges of compressive strength. Satakhun Detphan¹⁴, presents the fundamental data of fly ash based geopolymer mixed with the open-field rice husk ash, the basic properties viz., setting time, burning temperature of rice husk heap, temperature and pH during mixing were presented, furthermore, the 7 days strength of geopolymer mortar replaced by rice husk ash of 0, 20, 40 and 60% were also investigated. Gambhir¹⁵ investigated the contribution of fly ash (FH) to the positive effects in the strength in concrete has been attributed to direct water reduction, the increase in the effective volume of paste in the mix and its pozzolanic reaction . Its pozzolanic activity is due to the presence of finely divided glassy silica and lime which produce calcium silicate hydrate as is produced in Portland cement. Naidu¹⁶ investigated the influence of partial replacement of sand with quarry dust and cement with mineral admixtures on the compressive strength and pull-out force of concrete, whereas Celik and Marar¹⁷ investigated the influence of partial replacement of fine aggregate with crushed stone dust at varying percentages in the properties of fresh and hardened concrete.

Rice milling generates a by product known as husk. This husk is used as fuel in the rice mills to generate steam for the boiling process. This husk contains about 75% organic volatile matter and the balance 25% of the weight of this husk is converted into ash during the firing process, is known as rice husk ash (RHA). This RHA in turn contains around 85% - 90% amorphous silica. In present work 10% RHA is used as cement replacement material.

Carbon dioxide emissions are one of the most serious concerns among all greenhouse gas emissions. Carbon dioxide emissions can be affected by combustion of organic materials (e.g., wood, coal, oil and other fuels), or by human and animal metabolism (respiration) in which oxygen is utilized and CO₂ is given off as an end product. Also, dead animals, plants and other organic matter generate CO₂. Oil or coal burning power plants and cement-producing industries account for a large amount of CO₂ emissions. According to the statistics of the year 1998, 3.1% of the total CO₂ emissions were from the cement manufacturing industry (World Resource Institute). Approximately 88% of the CO₂ emitted and concrete industries is produced by cement production,1% is produced by concrete production, 9% by its use in construction, and 3% by demolition and waste handling. There exists an urgent need for a reduction in CO₂ emissions and/or recycling of CO_2. An effective method for the reduction of CO₂ in the environment is to store carbon dioxide librated from various industries and use that for curing of concrete. Chun Y.M.¹⁸, summarizes the results of an investigation on carbon dioxide (CO₂) sequestration in concrete. Kauer¹⁹ were cured the fresh concrete specimens in various humidities and temperatures in CO₂  atmospheres ranging from 4.5 to 18% for 24 to 96hr. concrete. Shao¹⁰ were investigated the feasibility of recycling carbon dioxide into concretes through their curing processes. Owens K J²⁰, has investigated the utilization of carbon dioxide from flue gases to improve physical and micro structural properties of cement and concrete systems.

Materials Used

Cement

Ordinary Portland cement of 53-grade was used in this study conforming to IS: 12269-1987. The physical properties are: Specific gravity = 3.15; Normal consistency = 28.3%.

Fly ash

Specific gravity of fly ash is 2.2 as per Specific gravity Test IS: 2386 (Part III) 1963.

RHA

RHA from the rice mill was used.10% RHA was considered in the present study as a replacement of cement. The specific gravity of RHA used is 2.0. The chemical composition of rice husk ash is shown on the right.

Fine Aggregate

The concrete mixes were prepared using river sand and CRP. The percentage of CRP by weight ranging from 0 to 100% as a replacement of sand was used in concrete. CRP is obtained from the nearby crusher units in Tumkur, Karnataka, India. Fineness modulus and specific gravity of the CRP are 2.78 and 2.63 respectively. Locally available river sand was also adopted to prepare reference mix for comparison purpose. Fineness modulus and specific gravity of sand are 2.9 and 2.64 respectively. The amount of fine particles present in CRP is considerably higher when compared to the river sand.

Coarse Aggregate

The blue metal was used as a coarse aggregate. Their specific gravity and water absorption are 2.67 and 0.4 % respectively. The tests were conducted as per IS: 383 – 1970²¹.

Water

In general, water fit for drinking is suitable for mixing concrete. Impurities in the water may affect concrete setting time and strength. Hence locally available purified drinking water was used in the present work.

Sambrani (Benzoin resin)

Sambrani is one of the oldest incense. It is a balanced resinaceous mixture of several elements derived from tropical wood, barks, roots, and resins. It is well used in Indian temples for worship.

Sambrani is burnt and the gas was collected in a standard flask to get solution. The solution is analyzed for its chemical composition. The major components are:

• CO₂ % is around 30 to 40 %.
• HCO₃ is less than 15 %.
• CO₃(carbonate) is around 21 %.
• Other aromatic hydrocarbons which are responsible for the pleasant smell of the Sambrani constitute remaining percentage.

Cement and Pozzolanic Reaction

If a concrete contains pozzolans like Fly ash and Rice husk ash, less cement is required to obtain a specified strength. A highly reactive pozzolan has more cementitious strength than a lower reactive pozzolan. Edwin R²² presents the pozzolanic reaction as follows:

In this reaction 222 parts of lime reacts with 120 parts silica for a mass ratio of 222/10=1.85. If a pozzolan is only 25% reactive and is combine with 0.46(%) of lime the reactive portion ratio is 0.46/0.25 = 1.4.

The relationship between lime and alumina is 222/102 = 2.18. Alumina combines with more lime than does silica.

Kauer¹⁹, presents the carbonation in cement-based products can be defined as a reaction between the CO₂ dissolved in water and the cement hydration product Ca (OH)₂ in the pore water. Since the gas is dissolved in water, the CO₂ is may be in the form of H₂CO₃, which in turn could react with the calcium ions of the pore water. The type of carbonate ions depends on the pH of the hydrated cement paste. When CO₂ comes in contact with water at neutrality it forms bicarbonate. Inside concrete the pH is high and the bicarbonate dissociates and forms carbonate ions. Thus in the carbonated layer bicarbonate forms (due to low pH) but closer to the uncarbonated cement paste. This carbonate ion forms and precipitates calcium carbonate crystals (CaCO₃).

Calcium carbonate exists in three crystallographic forms, viz. aragonite, vaterite and calcite. Calcite and vaterite are commonly found in carbonated concrete. Presumably the metastable vaterite will transform to stable calcite with time. These reactions can be expressed by equations (1) and (2).

CO₂ (g) + H₂O = HCO₃^-(bicarbonate ion) + H⁺ (1)

HCO₃^- = CO₃^2-(carbonate ion) + H⁺ (2)

The carbonate ion will react with calcium ions in the pore solution to form calcium carbonate (Eq. 3).

Ca²⁺ + CO₃^2- = CaCO₃ (3)

This will lead to lower concentration of Ca²⁺, which in turn will lead to dissolution of calcium hydroxide (CH). The solubility of calcium carbonate (CC) is much lower than that of CH.

Ca(OH)2 = Ca ²⁺ + 2 OH^- (solubility 9.95 x 10-4) (4)

Ca²⁺ + CO₃^2- = CaCO₃ (solubility 0.99 x 10 -8) (5)

Thus CH dissolves and CaCO3 precipitates and the process continues until all of the CH is consumed. Apart from CH the cement paste contains calcium silicate hydrate (C-S-H) and ettringite/monosulphate (AFt/AFm). All these phases are stabilized by high pH and Ca ions. Thus when the CH is consumed the C-S-H dissolves congruently. The percentage of above gases may vary with the brands. Darker the sambrani stick; higher is the percentage of CO₂ present in it.

Experimentation

Concrete Mix Proportions

M30 grade concrete mixes of different CRP levels and Fly ash levels (10% to 50% replacement of cement) and RHA of 10% with w/c ratio of 0.45 were prepared. The mixes were designated in accordance with IS: 10262-2009²³ and SP: 23-1982. The details of mix proportions with various curing methods are given in Table 1.

Specimen Preparation

Figure 1 · Cubes before 6 hr CO₂ curing

Figure 2 · Cubes during & after 6 hr CO₂ curing

The CRP was collected from local crusher units and Fly ash was collected from UltraTech Ready Mix Plant. Its properties were tested in the laboratory. The Fly ash, rice husk ash and cement were first dry mixed in a pan thoroughly so that a uniform mix of rice husk ash and cement is obtained. Fine and coarse aggregates were added together in the mixer. Then one third of the water is added. The mixture of rice husk ash and cement was then added into the mixer. The concrete was mixed in the mixer with all ingredients with addition of remaining quantity of water as per water binder ratio obtained by mix design. The mix was thoroughly mixed by rotating the mixer drum for more than two minutes. The specimens were finished smooth after giving sufficient compaction. The specimens were finished smooth after giving sufficient compaction. Specimens were prepared with water to cementations materials ratio of 0.45 with 100mm slump. Different batches were adopted for different ages of curing. The cube specimens were cast and tested for studying the variation in strength properties due to the replacement of sand with CRP after curing for required period as per IS: 516-1959²⁴.

Carbon Dioxide Curing

To enable accelerated carbonation of concrete (i.e., Carbon dioxide curing) specimens, a CO₂ chamber was constructed. Specimens stacked on racks made of perforated steel plates with sufficient gap for air circulation. A continuous CO₂ gas was maintained in the chamber by burning 10 sambrani sticks in 20 minutes intervals continuously for a period of 6 hours. After passing the carbon dioxide the cubes are turned to light white colour.

Figure 3 · Comparison of compressive strengths of concrete with
different CRP levels₂ curing

Figure 4 · Comparison of compressive strengths of WC concrete
v/s 6 hr CC and AC/WC₂ curing

Figure 5 · Comparison of compressive strength of concrete with
different FHRH levels₂ curing

Figure 6 · Comparison of compressive strength of WC concrete
v/s 6hr CC and AC/WC₂ curing

Results and Discussions

The Compressive strengths of WC Concrete in 28 days and CC and AC/WC are shown in Table 2 and Table 3. The compressive strength of RHRP concrete of M30 grade containing constant 10% cement replaced by Rice husk-ash and natural sand (fine aggregate) replaced by CRP up to 20% is found to be satisfactory with little constraint with age of curing.

RHC gain the highest strength (i.e., 53.44 % of the NC cured in water for 28 days) in 6 hr CC, 12 hr AC and 138 hr WC.
It is advantageous to have Rice husk-ash concrete with 10% level of CRP replacement (i.e. RHRP-10) which exhibits almost equal values of strength parameters to RHC concrete of same grade even at age of 28days and even this level of RHRP concrete is better than RHC concrete.
The other mixes higher than 20% CRP showed lesser compressive strength than the mixes with river sand. This can be due to the voids present in the concrete mixes with higher amount of CRP.

From Table 1 it was noticed that the NC, FHRH-10 and FHRH-40 concrete specimens have achieved required concrete strength at 28 days water curing.
From Table 2 it was noticed that all concrete specimens have achieved more than 50% designed strength at 6 hrs CC and 12 air curing. Compressive strengths of different CRP levels for different water curing periods are shown in Figure 3 and Figure 4 respectively. It was noticed that all concrete specimens have achieved more than 50% designed strength at 6 hrs CC and 12hrs air curing.

From Figure 3 and Figure 4, presents the comparison of compressive strength of concrete with water curing and CO₂ and air curing.
From Figure 5, it was observed that the FHRH-10 and FHRH-40 concrete specimens cured in water for 28 days exhibits higher strengths than other FHRH levels and slightly lower than the NC specimens.
From Figure 6, we see that more than 60% strength of M30 grade was achieved in 6hr CO₂ curing and 12 hrs air curing for the specimens of NC and FHRH-10 and FHRH-40.

It was noticed that, there was a saving of up to 22% when CRP replaced sand. Further there was a saving up to 40% in the curing cost. Addition of rice husk ash also has helped in reducing the cost up to 4.5%.
It is recommended to use fly ash and rice husk ash as partial cement replacement materials in concrete up to 40% fly-ash and 10% rice husk ash respectively without loosing its original strength and other durability parameters of concrete.

The chemical reaction involves fixing of Ca(OH)2 in liquid phase from the hydrating cement with the silica in the pozzolana. For lower percentage replacement level such as 10%RHA the silica from the pozzolana is in required amount. This aids the hydration process producing blocks with high compressive strength. For higher percentage replacement level, the amount of rice husk ash in the mix is higher than required to combine with the liberated calcium hydroxide in the course of the hydration. The excess silica substitute part of the cementitious materials and consequently causing a reduction in strength.

Conclusions

This paper has examined how CRP and FH and RHA and CO₂ curing affects the compressive strength and performance of concrete. The following conclusions can be drawn based on the experimentation in the laboratory:

• Pozzolanic reaction can significantly reduce the amount of cement and make concrete “green”.
• Fly ash and Rice husk ash can also make concrete “green” by reducing the water content which in turn reduces cement content.
• Minimum 45 % of 28 days strength of concrete achieved in 6 hr carbon dioxide curing and 12 hr air curing for all concrete (i.e., concrete with different CRP levels).
• RHRP-10 gain the highest strength (i.e., 107.73 % of the NC cured in water for 28 days) in 6 hr CC, 12 hr AC and 138 hr WC.
• 6 hr CC can brings about a reduction in the amount of chemically combined water in hardened cement paste.
• The flue gases have approximately 10 to 15% carbon dioxide content. This may suggest that flue gases can be used for a similar treatment instead of using 40% carbon dioxide from Sambrani smoke, thus reducing carbon dioxide being released into the atmosphere.
• The result suggests that proper use of CRP and FH and RHA can produce high performance concrete.
• It has also been found that the use of CO₂ curing increases the amount of calcium carbonate in the pore structure leading to a denser matrix, which may lead to an enhancement in durability of the mix.
• For a given mix, the water requirement increases as the rice husk ash content increases.
• Rice husk is available in significant quantities as a waste and can be utilized for making concrete blocks with higher percentages of RHA. This will go a long way to reduce the quantity of waste in our environment.

Acknowledgements

The authors wish to place on record their sincere thanks to Dr. Shivakumariah, principal, SIT, Tumkur and Dr. M.N. Channabasappa, Director, SIT, for providing facilities to prepare this paper. Many thanks are extended to Dr. S V Dinesh, Head, Department of Civil Engineering, SIT, for his encouragement during the development of this paper.

References