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Mitigation of GHG Emission and Assault on the Climate and the Environment with the use of PSWC-Bar -an Ideal Rebar for Durable Concrete Construction

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Anil K Kar

 

Dr. Anil K. Kar, B.Sc CE, MSCE, Ph.D.
Proprietor, Engineering Services International Kolkata, India

 

Abstract: Much international efforts are on-going to mitigate or minimize the generation of GHG. This article demonstrates a way to achieve this through minimization of the need for reinforced concrete constructions and therewith minimizing the manufacture of cement and steel for use in reinforced concrete constructions. This is achieved through several-fold enhancement of the life span of reinforced concrete constructions for which the production of cement alone leads to about 9.5 percent of the total global emission of GHG from all sources. The enhancement of the life span of concrete constructions is achieved with the use of PSWC bars of high strength steel, characterized by their plain surface and gentle wave-type configurations. Through several-fold enhancement of the life span of reinforced concrete constructions, the use of PSWC bars can greatly minimize the needs for frequent repairs and construction of replacement structures. The use of PSWC bars can thus greatly reduce GHG emission and other adverse impacts of construction on the climate and the environment. Besides the mitigation of GHG emission and the assault on mother earth through several-fold enhancement of life span of concrete constructions, all at no added effort or cost, the use of the highly innovative PSWC bar increases load-carrying capacities of concrete elements significantly and it reduces the life cycle cost of concrete constructions to a fraction of what it normally is. It transforms brittle reinforced concrete into ductile reinforced concrete with the potential to prevent catastrophies during earthquakes.

1 Introduction

Strength, easy formability, easy availability of the constituent materials and durability of earlier constructions made reinforced concrete the number one medium of construction.

Activities leading to such constructions, however, cause great harm to the earth, to its environment, and to the global climate.
The problem exacerbated following the start of use of ribbed reinforcing bars (rebars) of high strength steel, where the high strength in steel bars is achieved with higher carbon contents and additionally subjecting the bars to cold working as in the case of CTD bars or subjecting the bars to a process of quenching or thermal hardening as in the case of TMT bars.

According to latest figures, around one-third of carbon emissions in the UK come from the built environment, including raw material production, construction, operation, maintenance and decommissioning.

One simplistic way to reduce the GHG generation would then be to stop further construction. But that would not be acceptable.
The alarming situation recently led the UK Parliament to declare a climate emergency.

This alarming situation has also made the US Congress ask the President of the USA to turn back and abide by the Paris Accord.
Much earlier, in its 2014 report, “Trends in Global CO2 Emissions — Background Studies,” the PBL Netherlands Environmental Assessment Agency [1] had reported that the making of just one element, cement, a principal constituent element of reinforced concrete, led to 9.5 percent of the total global emission of CO2 from all sources.

It is easily recognizable that besides the CO2 emission from cement manufacturing, reinforced concrete construction entails enormous demands on the nature resources.

Additionally, there is very considerable direct warming of the air through activities related to quarrying, transportation, processing/manufacturing of the construction materials, and the activities directly related to construction.

And, compared to constructions of earlier periods, today’s reinforced concrete constructions with ribbed CTD or ribbed TMT bars, suffer early decay, distress and demolition or collapse (Papadakis, et al. [2], Central Public Works Department [3], Swamy [4], Alekseev [5], Kar [6, 7 and 8]).

That is not all. The disposal of materials from fallen structures too adds to adverse impact of construction on the environment. This aspect of concrete construction has gained greater significance these days as more and more concrete constructions with ribbed rebars are requiring early repair or demolition and disposal.
In spite of all such adverse effects of construction (mostly reinforced concrete construction) on the global climate and the local environment, many nations appear to have pressed on the accelerator pedal for construction in the hope of greater economic progress, causing greater and greater harm to the climate and the environment when the air is already crying out for help.
The resulting natural events in recent years would suggest that the climatic balance might have been lost.

2. A Possible solution to the problem of adverse impact of concrete construction on the climate

In the dismal scenario, identified above, reinforced concrete being both the number one medium of construction, as well as being one of the topmost polluting agents, a way had to be found to minimize the adverse impact of reinforced concrete construction on the local environment as well as on the global climate.

It would help if the minimization of the adverse effects of reinforced concrete constructions on the climate and the environment would require no extra effort or cost.
This is achieved through the use of the highly innovative and award-winning (e.g. Henry L. Michel Award for Industry Advancement of Research in 2015 from the American Society of Civil Engineers, USA, etc.) PSWC bar [Kar 7, 8] (Figure 1), which is characterized by its plain surface and a gentle wave type configuration, as opposed to today’s ribbed CTD or TMT bars (Figure 2).

Figure 1 PSWC bar of steel characterized by plain surface and gentle wave type configuration
Figure 1 PSWC bar of steel characterized by plain surface and gentle wave type configuration

 

 

 

 

 

 

 

3.0 PSWC bar for the mitigation of GHG emission

The PSWC bar (Figure 1) is a highly innovative concept in reinforced concrete constructions, as, though its use as a reinforcing bar greatly improves the all round performances of reinforced concrete constructions, viz., several-fold enhancement of life span, ductility and energy-absorbing capacities as well as very significantly higher load-carrying capacities [7, 8, 9, 10, 12, 13], lowering of GHG emission and demand on nature resources, it requires no new material and its manufacturing or use requires no new technology.

In order to minimize corrosion at accelerated rates in today’s rebars, and thus to enhance the life span of reinforced concrete constructions several fold, PSWC bars of high strength steel are made to have a plain surface [Kar 7,8,9]. Additionally, in order to improve bond or engagement with concrete, and thus to enhance the all-round performances of reinforced concrete constructions under load [9], PSWC bars are given a gentle wave-type configuration along the length (Figure 1).

The essence of the innovation in PSWC bar thus lies in the coupled effects of (a) absence of ribs on its surface, and (b) the presence of a gentle wave-type configuration along the length.
The material of PSWC bar is steel of grades which are used in the manufacture of hot rolled products. In due consideration of durability and safety of concrete structures in seismic environments, the material should have high percent elongation. Thus, the yield strength of the steel may not exceed 550 MPa, or better still 500 MPa, and more importantly this strength shall not be achieved through cold working or through quenching at a hot state.

In essence, the PSWC bars are hot rolled, the yield strengths in such bars are kept within bounds such that the % elongation or ductility will be high, and the service/working stresses are kept low such that the structures will last longer. Recommended mechanical properties of steel for PSWC bars are given in Table 1.
It need to be recognized here that structures that last longer reduce environmental footprint. Constructions with longer life spans mean that the total of GHG emission and other emissions, attributed to heating, can be thought of as being spread over a much longer period of time.

3.1 Physical characteristics of PSWC bar

The pitch length, defined as the distance between two successive peaks on the same side of the axis of the deformed configuration of the PSWC bar (Figure 1(b)), is 20d to 30d (30d for standardisation), where d is the diameter of the bar, and the offset or peak excursion of the axis of the PSWC bar from its original straight line is about 4 mm to 6 mm; 5 mm for standardisation.

Even though offsets, 6 mm and higher, have led to better performances under load, the recommended configurational proportions provide PSWC bars with gentle configurations, and make the use of such bars more practical. It is recognized here that, according to provisions in some Standards, 5 mm is the permissible deviation in the placement of rebars from their stated positions.

The principal objective behind the innovation of PSWC bar was to make reinforced concrete constructions much more durable than these are built to be these days, and therewith minimize the many shortcomings of today’s reinforced concrete constructions which reach states of decay, distress and failure early.
It is recognized in this context that higher the yield stress, less is the ductility or % elongation of the rebar as well as resistance to corrosion. All of these lead to smaller life spans of concrete constructions as well as lower resistance of structures to seismic forces.

3.2 Mechanical properties of PSWC bar

Most important in the interest of sustainability and durability of concrete structures through minimization of the rate of corrosion in rebars are the requirements that (a) the surface of PSWC bars shall be plain, (b) the limiting yield strength shall be a maximum of 550 MPa or preferably a maximum of 500 MPa, and (c) the high yield strength must be achieved through appropriate chemical composition of the materials rather than through the conventional practices of cold working or thermal hardening.

3.3 Manufacture of PSWC bar

PSWC bars are made easily by making a small change in the last stand of the rolling mill process for conventional ribbed rebars. The pair of rollers, used to create the ribs, are replaced with a contraption of appropriate design to give wave-type configurations to the rebars.

4.0 How does PSWC bar mitigate GHG emission

In the absence of secondary stresses, which could have arisen due to any provision and presence of ribs on the surface, stresses and strains in PSWC bars under service load conditions are much less than the yield stress or strain (as per design), and such bars, with their plain surface, are thus passivated and better protected against corrosion inside concrete when cement will be of the right type, e.g., Ordinary Portland Cement.

Highly corroded ribbed bars (Figure 2) cannot be passivated.
Thus, in sharp contrast to PSWC bars, conventional ribbed bars, with stresses or strains at or beyond yield inside concrete, will remain unguarded against corrosion for lack of passivation.

Fontana [11] provides an estimate of the differences in the rates of corrosion in passivated and non-passivated steel thus: “It is important to note that during the transition from the active to the passive region, a 103 to 106 reduction in corrosion rate is usually observed.”

On the basis of extensive work in Russia, Alekseev [5] commented: “the durability of reinforcement specimens with a stepped (deformed) profile may be roughly an order less than that of smooth specimens since the former have stress concentrators on the surface at the bases of projections, which represent sites of preferential formation of cracks.”

Concrete structures, built with plain bars, as PSWC bars (Figure 1) will thus have life spans several times longer than those of concrete structures, built with today’s ribbed bars (Figure 2).

 

Table 1
Table 1: Mechanical properties of steel in PSWC bar

 

 

 

 

Simultaneously, given its gentle wave-type configuration, the effective bond or engagement between PSWC bars and the surrounding concrete is greatly enhanced, as should be evident from a comparison of the information available in Figure 3, Table 2, Table 3, and as shown by Kar [9].

As the PSWC bar is devoid of any surface feature, as the strength in the material for PSWC bar is not gained through the violent CTD or TMT process, and as its use improves the load-carrying capacities of reinforced concrete elements, it fully and eminently meets the required objectives of the innovation in solving the world-wide problem, in all its manifestations, of early decay and distress in today’s reinforced concrete constructions with ribbed CTD and TMT bars.

Table 2
Table 2. Load carrying capacity of beams

 

 

 

 

 

 

4.1 PSWC bar meets the tests for durability economy safety and sustainability of concrete Constructions as a way to mitigate GHG emission

The several fold increase in the durability of concrete constructions with PSWC bars leads to significantly lowered GHG emission, and assault on the climate and the environment in the long run. As opposed to reinforced concrete constructions with today’s ribbed rebars, the several fold increase in the durability of concrete constructions with PSWC bars leads to greater economy, long term safety and greater sustainability of concrete constructions, reinforced with PSWC bars.

4.2 PSWC bars meet the tests for durability, economy, safety and sustainability of concrete constructions as a way to mitigate GHG emissions

The use of PSWC bars, bereft of ribs on the surface, and free from the ill effects of cold twisting or thermal hardening in causing corrosion at accelerated rates, eliminates the two basic causes of the world-wide problem of early decay and distress in today’s reinforced concrete constructions. It does much more. Tests have revealed that the use of PSWC bars increases load-carrying capacities in both beams and columns (Table 2 and Table 3).
A comparison of results of tests on flexural members is offered by Aarathi [10] in Figure 3.

 

The ultimate load-carrying capacity of the beam with conventional reinforcement was 237.10 kN, whereas the ultimate load-carrying capacity of the beam with PSWC bars, having the same strength properties as those of the conventional reinforcement, was 330.60 kN, indicating an increase of 39%, that was achieved simply by giving a gentle wave-type configuration to the bars.
A comparison of test results in Figure 3 shows a dramatic increase in the ductility and energy-absorbing capacity with the use of PSWC bars.

Results from a few of the many tests, involving under-reinforced beams (Patel [12]) can be found in Column (5), Table 2. The increase in the load-carrying capacity of a beam with PSWC bars (Sl. No. 2) was (154.67-109.00) (100.0÷109.00) or 42% over the load-carrying capacity of a beam with plain round bars (Sl. No. 1). This 42% increase in the load-carrying capacity, observed by Patel [12], compares with the 39% increase as per Figure 3(a) and Figure 3(b), observed by Aarathi [10].

The 42% increase, as observed in the work of Patel [12], is highly conservative as the limitations of the test facilities did not permit Patel to study the post-yield response.

It is seen in Column (6) of Table 2 that when the yield strength of all bars are assumed to have yield strength of 576.79 MPa, matching that of the HYSD Fe 550D ribbed bar in Sl. No. 6, the Achievable Ultimate Load of beams becomes the highest in the case of PSWC bar with 5 mm offset at 274.12 kN.

A comparison of the load-carrying capacities of beams, given in Column (6), Table 2, shows that when ribbed bars (Sl. No. 6) may be replaced with PSWC bars (Sl. No. 2), having the same yield strength for both types of rebars, there may be an increase of about (274.12 – 238.33) (100.0 ÷ 238.33) or 15%.

The increase of 15% does not take into account the fact that the real ultimate load in the case of the beams with PSWC bars at their post-yield state can be much higher than the normalized load of 274.12 kN at yield as could be seen from a comparison of results in Figure 3(a) and Figure 3(b).

It is also seen in Column (7) of Table 2 that the ratio Experimental Ultimate Load to Analytical Ultimate Load is the highest at 2.98 in the case of beams reinforced with PSWC bars with 5 mm offset.

Setting aside the very significant improvement in post-yield performance of beams when PSWC bars are used as rebars, the information in Columns (6) and (7) in Table 2 clearly shows the best load-carrying capacities of reinforced concrete flexural elements when PSWC bars are used as rebars.

All these show that concrete flexural elements can be most economically constructed when PSWC bars will be used as rebars thereby satisfying the sustainability criteria of economy.
Alternatively, using the same quantities of materials, but with PSWC bars, instead of any other rebar, highest safety can be built into structures thereby satisfying the sustainability criteria of safety.

Similar to the case of flexural elements, a review of the information on columns in Table 3 clearly shows the benefits of using PSWC bars as rebars in the construction of columns. If PSWC bars in the columns in Sl. No. 2 would have steel with fy of 435 MPa, and if the cube strength of concrete would have been 37.78 MPa as in the case of columns in Sl. No. 3, the test load of columns with PSWC bars could have been even higher at 1635.0 kN instead of 1586.67 kN.

Table 3
Table 3. Failure loads of columns when tested

 

 

 

 

The results from column tests (Table 3), and additional tests (Varu [13]) and Kar, et al. [14]) on columns with PSWC bars, but without any ties, suggest that (a) there may not be any premature buckling of the PSWC bars under compression, and (b) as in the case of beams, the quality of engagement between concrete and rebars influences the load-carrying capacity of columns (Kar [9]), and, among rebars of different types, the use of PSWC bars leads to the highest load-carrying capacity in the case of columns (Kar [8,9, 13, 14]).

It may be mentioned here that (a) the basic data in Table 3 are taken from a thesis by Varu [13], who had tested 33 columns with 11 different types of rebars. The inclusion of performance data of the remaining 24 columns with 8 other types of rebars would not have changed the nature of findings in Table 3. More details on the performance of 33 columns have been provided by Kar, et al. [14] and by Kar [8, 9].

Tests by Varu [13] showed that (a) if there would be no ties around the vertical rebars, the bursting (mode of failure of short columns under axial load) load would be less, and (b) with increasing offsets in the configuration of PSWC bars, i.e., with increasing engagement with concrete, the bursting load would increase, confirming thereby that the wave pattern of PSWC bars would not lead to buckling of such bars in compression elements.
Many studies on beams and columns were made at different universities. In the tests, many types of bars of different diameters, different steel grades and different surface conditions and configurations were used. Tests consistently showed better structural performances with the use of PSWC bars.

Since PSWC bars have a plain surface, since the violent CTD and TMT processes are avoided in achieving high strength in the rebar materials, since the % elongation is higher in the case of PSWC bars (Table 1) and thus their susceptibility to corrosion is much less than the susceptibility (to corrosion) in today’s ribbed bars, since, in terms of load-carrying capacity, beams and columns, reinforced with PSWC bars, at no added effort or cost, outperform beams and columns, reinforced with conventional rebars, whether plain or ribbed, PSWC bar not only meets the test for durability, which is the primary objective behind its development, it also meets the tests for load-carrying capacity, economy and increased safety. Thereby, the use of PSWC bar not only aids sustainability of concrete construction, the development of PSWC bar has turned out to be a great innovation in climate action as for this great action in the benefit of the climate and the nature no extra effort or expenditure is involved beyond what would have been normally required to make reinforcing bars of steel for concrete construction.

4.3 PSWC bar meets the tests for increased ductility energy-absorbing capacity and sustainability

As can be seen in Figure 3, the use of PSWC bars increases ductility and energy absorbing capacities of flexural elements of reinforced concrete very significantly.

While the displacements at yield and at failure in the case of the control beam with conventional plain round bars were 5.39 mm and 6.97 mm, without any increased load-carrying capacity beyond yield (Figure 3a), the corresponding figures for the beam with PSWC bars of the same material (Figure 3b) were 5.42 mm and 21.5 mm, with increasing load-carrying capacity beyond yield, a characteristic of true ductile behavior.

The comparisons show that while the ductility became higher at 3.1 times, the energy absorbing capacity increased to a level that was higher at 6.0 times when PSWC bars were used as rebars.
Tests on many more beams, straight and cambered, showed similar trends: brittle failure in the cases of beams with conventional plain bars and ductile failure in the cases of beams with PSWC bars.

The use of PSWC bars as rebars thus transforms traditionally non-ductile reinforced concrete into ductile reinforced concrete, with several hundred percent higher energy-absorbing capacities thereby making concrete structures safer during overload and much better resistant to forces during earthquakes and other dynamic loadings. This transformation of traditional rein forced concrete elements into truly ductile reinforced concrete elements, with the use of innovative PSWC bars as rebars, at no added effort or cost, makes reinforced concrete constructions much more sustainable than it was possible ever before, contributing thereby immensely to environmental and climate benefits as well as to economic and social conditions.

4.4 PSWC bar meets the tests for earthquake resistant constructions

Tests have shown that, besides significantly higher load-carrying capacities beyond yield of steel in rebars, concrete beams, reinforced with PSWC bars, have ductility several times that of concrete beams, reinforced with conventional plain round bars. The relative increase in energy-absorbing capacities is even higher.

Ribbed CTD or TMT bars have been necessarily kept out of consideration in the study of relative performances in earthquake environments for two reasons:

a) the use of ribbed CTD and TMT bars has led to early decay and distress in reinforced concrete constructions to great detriment to the climate, to the environment, and to economic and social causes
b) the susceptibility of ribbed CTD and TMT bars to corrosion at accelerated rates (Figure 2), and the failure of such highly corroded bars to be passivated inside concrete make such bars corrode excessively inside concrete thereby weakening such constructions
c) weakening of structures leads to lowering of resistance to earthquake and other forces
d) PSWC bar has been innovated as a solution to the myriad problems which have been caused or can be caused by the use of today’s ribbed CTD and TMT bars.
The greater ductility and energy absorbing capacities of reinforced concrete elements, as made possible by the use of PSWC bars, are very important elements in minimizing the damaging effects of earthquakes on structures and consequently on the environment.

Among reinforcing bars of different types, PSWC bar thus admirably satisfies the test for earthquake resistant constructions, with potentials to prevent catastrophic losses to lives and properties, leading thereby to enormous possible benefits to environmental, economic, and social conditions.

4.5 PSWC bar meets the tests for increased life span and lower life cycle cost

By virtue of the fact that concrete structures, reinforced with PSWC bars, characterized by their plain surface, will have much greater life spans, constructions with PSWC bars will have significantly lower life cycle costs. Life cycle costs can be lowered further by taking advantage of the increased load-carrying capacities of concrete flexural and compression elements by using PSWC bars as rebars, and also by taking advantage of the power of PSWC bars in transforming brittle reinforced concrete into ductile reinforced concrete. PSWC bar thus admirably satisfies the sustainability criteria of lower life cycle cost as well as benefits to environmental, economic, and social conditions.

4.6 Test for ease of design and construction

Students at different universities have successfully designed and constructed numerous beams and columns with PSWC bars as with conventional plain bars and ribbed bars using the Indian standards. They encountered no difficulties, either in design or in construction with PSWC bars.

For positional locations (e.g., effective depth) in design, the PSWC bars were considered as if there was no deformation of the axis.

This should suggest that the use of PSWC bars is not beset with any unusual problem in design and construction.

5. How PSWC bar mitigates GHG emission and minimizes adverse impacts of reinforced concrete constructions on climate and environment

The problem with reinforced concrete constructions came to the fore and the great concern arose following the use of ribbed rebars, particularly when the strength of such bars was enhanced with increased carbon contents and simultaneously such bars were twisted beyond yield at a cold state (CTD bars) or the bars were quenched at a hot state in processes known as thermo mechanical treatment (TMT) or thermal hardening.

The innovation of the PSWC bar (Figure 1) has its basis in the recognition of the inherent susceptibility of ribbed bars to corrosion at accelerated rates (Figure 2) and the consequent early decay and distress in concrete structures, reinforced with such bars, as reported by Alekseev [5], Kar [6, 7,8 and 9]and others.
PSWC bar (Figure 1) addresses, at no added effort or cost, the problem of early decay and distress in reinforced concrete constructions with ribbed CTD (cold twisted deformed) and TMT (thermo mechanically treated) bars (Figure 2). It helps lengthen the life span of such structures several fold. It significantly increases load-carrying capacities of concrete elements (Figure 3, Table 1 and Table 2), and it makes reinforced concrete elements ductile through several-fold enhancement of ductility and energy-absorbing capacity (Figure 3).

All these positive attributes of PSWC bar, more particularly, its use leading to several fold enhancement of life span of concrete structures help to minimize very considerably the adverse impact of concrete constructions on the local as well as the global climate, including about 9.5 percent of the total global emission of CO2 from all sources. These positive attributes also lessen destruction of the environment.

6. PSWC bar aiding the cause of the climate and the environment through improved ductility and energy-absorbing capacity of concrete constructions

Kar [8, 9] has presented data showing that, besides several-fold enhancement of life span of concrete structures, the use of PSWC bars also leads to several-fold increase in ductility and even greater enhancement of energy-absorbing capacity of reinforced concrete elements.

Kar [9] has suggested that the poor ductility of reinforced concrete constructions with today’s rebars could possibly be due to the inability of conventional steel rebars, plain or ribbed, to intimately and sufficiently engage inherently brittle concrete; failing thereby to provide a good resistance to the propagation of cracks across the rebars into the mass of concrete in the compression zone, leading thereby to an early and sudden failure of the member under load, as the member is found incapable of sustaining such load through continued deflection of the member once the yield load is reached (Figure 3(a), Aarathi[10]). [Note: PSWC bar was initially referred to as C-bar]

In sharp contrast, a ductile member continues to sustain increasing load, beyond yield of steel reinforcement, through continued deflection (Figure 3(b), Aarathi[10]).

The rebars for the beams in Figure 3(a) and in Figure 3(b) were the same, except that the bars for the beam, related to Figure 3(b), were PSWC bars (Figure 1). The dimensions of the beams and the concrete properties were the same in the two cases.
Figure 3(a) shows the load-displacement curve for a beam where the load reached a peak of 237.1 kN which happened when the stress in the steel rebars reached the yield stress level.

In sharp contrast, the beam, represented in Figure 3(b), did not fail when the stress in the rebars reached yield stress level. The beam continued to carry greater loads until it failed at a load of 330.0 kN. The maximum displacement at failure was 21.50 mm (Figure 3(b), compared to the maximum displacement of 6.97 mm in the case of the conventionally reinforced beam in Figure 3(a). Figure 3(a) and 3(b) are plotted to different scales.
The ductility in the case of the conventionally reinforced concrete beam was 1.0 (Figure 3a). In comparison, the ductility in the case of the beam with PSWC bars was 3.1 (Figure 3b).

Similarly, the energy-absorbing capacity in the case of the conventionally reinforced beam was 882kN-mm and six times higher at 5280 kN-mm in the case of the beam, reinforced with PSWC bars.

Similar observations of significantly greater load-carrying capacities, and several times higher ductility ratios and even higher energy-absorbing capacities were made by others too when PSWC bars were used instead of conventional plain round bars (Kar [9]).

Table 2 and Table 3 show results of tests on some representative beams and columns, reinforced with different types of rebars.
Even without taking into consideration the post-yield ductile performances of flexural elements, reinforced with PSWC bars, best performances, measured in terms of experimental ultimate load/analytical ultimate load ratio, was always the best when PSWC bars were used as reinforcement in beams and columns.
The PSWC bar can thus improve the survivality of reinforced concrete constructions during earthquakes and thus avoid the need for construction of replacement structures which would have meant a great cost to the climate and the environment, besides to the society and the economy.

7. PSWC bar in aid of climate through minimization of greenhouse gas emission and assault on the climate

The world-wide problem of early distress in today’s concrete constructions has led to a serious environmental issue because of the demand for additional manufactured materials and nature resources for repair and early construction of structures as replacement for the failed structures.

The PBL Netherlands Environmental Assessment Agency [1] has reported that the making of cement, a principal constituent element of reinforced concrete, leads to 9.5 percent of the total global emission of CO2 from all sources.

There is also emission of SO2 in making steel for reinforcing bars, and there can be emission of CO2 in producing electric power in making steel and reinforcing bars. The high level of carbon assessment, associated with the built environment in the UK has already been recorded.

All of these suggest that the use of PSWC bars, which can increase the life span of concrete structures several fold, which may prevent catastrophic failures of structures during earthquakes, and which increases the load-carrying capacities of concrete elements, can help (a) minimize GHG emissions by about five percent of the total global emission of CO2 from all sources and(b) minimize assault on the climate and the environment.

And this is possible without any extra effort and without any extra expense. In fact, it is possible at less cost as the use of PSWC bar increases the load-carrying capacities of reinforced concrete elements.

8. PSWC bar in aid of the environment

Like any other construction, today’s reinforced concrete construction by itself, coupled with the sourcing and hauling of the mined non-renewable materials, manufacturing and transportation of the constituent elements, which go into the making of reinforced concrete construction, make great demands on the environment.

The problem has been magnified several fold unnecessarily and unintelligently by the poor choice and use of ribbed CTD and TMT bars as reinforcing bars thereby causing early decay, distress and demise of reinforced concrete constructions, thereby increasing the demand on resources of the nature.

As the use of PSWC bars, as opposed to conventional rebars, can enhance the load-carrying capacities of concrete constructions, and as the use of PSWC bars can increase the ductility, energy-absorbing capacity and life span of concrete structures several fold, it can thus lessen the demand on the environment very considerably through very significant minimization of the demand on nature resources over a period of time.

9. Concluding remarks

Men of wisdom are concerned at the continuing GHG emission and assault on the climate and the environment in various ways.
It has been recognized that the all-too-common reinforced concrete construction is greatly responsible for much of the assaults on the environment and the climate.

The use of PSWC bar, characterized by its plain surface and a gentle wave-type configuration along the length, can over a period of time, mitigate about five percent of the total global emission of GHG and other assaults of reinforced concrete construction on the climate and the environment.

The use of the award-winning PSWC bar, instead of conventional ribbed bars, makes possible the mitigation of GHG emission, through several-fold enhancement of life span of concrete structures, several-fold increase in ductility and energy-absorbing capacity of concrete flexural elements, and through significant increase in load-carrying capacities of concrete flexural and compression elements.

The use of PSWC bar of high strength steel, as reinforcing bar in concrete construction, requires no additional effort, material or cost to bring about all-round improvement in the performance of reinforced concrete construction and at the same time minimize the adverse impacts of reinforced concrete constructions on the environment and the global climate.

References

1. PBL Netherlands Environmental Assessment Agency, Trends in Global CO2Emissions, Report — Background Studies, 31, 2014.
2. Papadakis, V.G., Vayenas, C. G. and Fardis, M. N., “Physical and Chemical Characteristics Affecting the Durability of Concrete”, ACI Materials Journal, American Concrete Institute, March – April, 1991.
3. Central Public Works Department, Government of India, Technical Circular 1/99, No. CDO/SE(D)/G-291/57, dated 18/02/1999.
4. Swamy, R. N., “Infrastructure regeneration : the challenge of climate change and sustainability – Design for strength or durability ?”, The Indian Concrete Journal 81(7), 2007.
5. Alekseev, S. N., “Corrosion of Steel Reinforcement,” Durability of Reinforced Concrete in Agressive Media, Oxford & IBH Publishing Co. Pvt. Ltd, New Delhi, India, Chapter 7, pp. 164-247, 1990.
6. Kar, A. K., “Concrete structures – the pH potential of cement and deformed reinforcing bars,” Journal of the Institution of Engineers (India), Civil Engineering Division, Calcutta, Vol. 82-6, pp. 1-13, 2001.
7. Kar, A. K., “Improved Rebar for Durable Concrete Constructions,” New Building Materials & Construction World, 16 Issue-1, pp.180-199, July, 2010.
8. Kar, A. K., “A Reinforcing Bar for Durable Concrete Constructions and Much More,” The Masterbuilder, 20(9),pp.136-146, September, 2018.
9. Kar, A. K., “A theory on the performance of reinforced concrete elements,” Proceedings of the Institution of Civil Engineers — Construction Material, https //doi.org/10.1680/jcoma.18.00019, 2018.
10. Aarathi, A. R. V., Optimization of C-bars for enhanced flexural performance of RCCbeams, M. Tech Thesis, B.S. Abdur Rahman University, Chennai, 2014.
11. Fontana, M. G., “Corrosion Engineering,” Third Edition, McGraw Hill Education (India) Private Limited, New Delhi, 2005.
12. Patel, N. A., Study on PSWC-bar as Reinforcement for Beam, M. Tech. Project, Nirma University, Ahmedabad, India, 2015.
13. Varu, R. S., Studies on C-bar as reinforcement for column, M. Tech. Project, Nirma University, Ahmedabad, 2014.
14. Kar, A. K., Dave, U. V, and Varu, R. S., “Performances of columns reinforced with PSWC-bars and other rebars,” The Indian Concrete Journal, 92(7), pp. 12-17, 2018.

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