1 Introduction

In today's era, where more than half of the world's population lives in urban areas, a sizable fraction of population is either homeless or lacks structurally safe and affordable housing meeting minimum standards of occupancy and sanitation. India, with over 1.4 billion population, is anticipated to undergo rapid economic growth over the coming decades in view of its demographic advantages. To address nation's housing and long-term infrastructure needs, the Indian government has adopted the motto "Housing for all". However, the current practice of proliferation of concrete jungles for meeting ever increasing infrastructural demand, especially housing, has severely impacted earth’s environment. One of the most unwelcome effluents of the cement and the steel industries is carbon dioxide (CO2), which unavoidably has a cascading impact in terms of global warming, coupled with aftereffects such as rising sea levels, floods and famines. Environmental experts have estimated that for every ton of cement and steel produced, at least half ton and one ton of CO2 are released, respectively [1, 2]. According to the global status report for buildings and construction [3], the construction sector accounted for 39% of energy and process-related CO2 emissions in 2018, 11% of which resulted from manufacturing building materials such as steel, cement and glass. Sulphur dioxide (SO2) and nitrogen dioxide (NO2) are other prominent effluents from the cement industry. Similarly, benzene toluene xylene (BTX), polycyclic aromatic hydrocarbons (PAH), cyanide, ammonia, phenols, and cresols are other noticeable hazardous compounds originating from the steel industry.

Looking back at the traditional house building practice, the use of wood/timber had been very popular for being durable and eco-friendly. Although wood is a non-polluting building material, it regenerates very slowly. A typical timber grade tree takes 15–25 years to grow to harvestable level. Large scale use of timber has upset the ecological balance in several parts of the world by severe deforestation. For a country like India, where the total forest cover is only 713 thousand square kilometres, representing 21.67% of the country's total geographical area [4], using wood/timber on a large scale is neither feasible nor sustainable.

On the other hand, bamboo, biologically a “grass”, absorbs much more CO2 from the atmosphere per unit mass than a typical wood tree. Also, compared to trees, it produces 30% more oxygen [5]. Some bamboo species can absorb up to 12 tonnes of CO2 per hectare per year, rendering bamboo a highly carbon-negative building material and an efficient oxygen replenisher. In just three to five years, bamboo matures to a natural structural material that is lightweight and functionally graded for the building sector. Therefore, bamboo's economic value is believed to increase if civil engineers start employing it for construction. In India, small farmers have started investing in bamboo plantings with the assurance that the demand is likely to increase and their financial prospects will improve.

A number of studies can be found in the literature related to mechanical properties of bamboo especially its strength characteristics. Bamboo fibres, chemically or mechanically retted from the culm (species Neosinocalamus affinis), possess tensile strength as high as 930 MPa [6]. However, the overall strength of a raw bamboo culm is much lower and is a function of the species, moisture content, age and wall thickness. Experiments conducted on species Phyllostachys edulis reveal that tensile strength typically decreases as moisture content falls below the fibre saturation point, usually in the range of 20% to 30%, depending on the species [7, 8]. Comprehensive tests by Madhusudan et al. [8] have indicated large-scale variability in bamboo’s material and mechanical properties depending upon growth conditions, location along the culm, geometric imperfections and environmental conditions. It is also reported that the compressive and the tensile strength increases with increase in the wall thickness and the outer circumference [9]. Owing to growing importance of bamboo as a structural material, the Bureau of Indian Standards has formulated a new code of practice, IS 15912, in 2018 for structural design using bamboo [10]. More than 100 species of bamboo are native to India. Twenty species have been systematically tested, out of which sixteen species of are recommended for structural applications by IS 15912. The code recommends that matured bamboo of at least four years of age should be used at least six weeks after the felling period. The code lists the strength and the elastic properties of various Indian species. The code listed compressive strength values lie between 35 to 70 MPa. Safe permissible stresses are also recommended species wise considering partial factor of safety between 3.5 and 4.5. However, despite the advantages from environmental and strength considerations, before bamboo can be accepted by mainstream structural engineers and builders, studies are needed to enhance its structural performance, long term durability and construction technology amenable for industrialization [11]. This is especially important since single shoot bamboo is very slender resulting in very low allowable compressive stress despite much higher fiber strength.

While bamboo culm is a potential structural material for main load bearing framing system, cow-dung, a waste product from the dairy industry, offers itself as a building material suitable for walls and partitions, surface painting and plaster [12]. Cow-dung contains a significant amount of fibrous material, including cellulose, lignin, and hemicellulose, which imparts it good compressive strength upon drying. Malik [12] successfully demonstrated use of cow-dung bricks, manufactured from cow dung, clay, and lime as eco-friendly construction elements which can be utilised for various purposes, including wall panelling and masonry. The advantage of the cow-dung bricks is zero additional carbon emission and zero thermal energy input in the manufacturing process as they are not burnt. Similarly, the cow-dung based mortar, again constituted using cow-dung, lime and water, can reasonably reduce the demand for cement and riverbed sand, thus positively contributing to green development [12]. Several studies have been reported from other parts of the world also on use of cow-dung as a constituent of composites. Yusefi et al. [13] investigated the performance of cow-dung reinforced poly lactic acid bio-composites for potential use in load bearing applications. Addition of cow-dung to poly lactic acid led to an improvement in the flexural and dynamic mechanical properties while reducing the tensile strength. Patel et al. [14] demonstrated replacing high-cost silica sand with sustainable eco-friendly cow-dung for sustainable moulding and casting in the foundry industry. Wu et al. [15] extracted natural lignocellulosic fibre from cow-dung for potential use as reinforcing material in resin-based polymer composites for the automotive component industry. The same were found to be promising candidate in terms of strength and other mechanical parameters. As per statistics, the estimated total wet cow-dung production in India is 562 million tonnes [16]. While its usage for generating biogas is on rise, its potential as building material in the form of unburnt bricks and mortar is yet to be explored. Studies are severely lacking on long-term structural and environmental performance of cow-dung based bricks and mortar before it can be adopted by the construction industry.

Following sections of this article present the developmental background, component level structural evaluation, design and construction of a structurally safe prototype structural unit using bamboo composite elements and cow-dung bricks to demonstrate an affordable alternate sustainable technology for achieving near zero operational and embodied carbon on the lines of India's goal of achieving net-zero emissions by 2070.

2 Fibre reinforced bamboo composite: development and structural evaluation

Fibre reinforced bamboo composite (FRBC) is a novel structural composite produced by the amalgamation of multiple bamboo culms in a cohesive matrix, bound together by a mixture of polypropylene fibres and an epoxy-based adhesive. The proprietary process, registered with the Indian patent office [17] unifies an m \(\times\) n group of naturally varying bamboo culms into an aggregated rectangular configuration circumventing the problem of high slenderness of single shoot bamboo, thereby achieving a regular unified prismatic member, as shown in Fig. 1 [18]. FRBC acts as a composite unit with less variable structural properties under applied loads, thus providing resistive capacity to axial force, shear forces and bending moments comparable to reinforced concrete (RC) elements [18].

Fig. 1
figure 1

Fibre reinforced bamboo composite (FRBC), Indian patent application no. 202211056213

Full size image

Its high flexural capacity and composite behaviour have been experimentally validated through multiple tests at the Structural Engineering Laboratory, Indian Institute of Technology Delhi. Detailed fabrication cum experimental testing procedure, observations and results covering three FRBC beams have been published by authors [19], only a brief summary is presented here. Culms of the species Dendrocalamus strictus, having an average outer diameter of 40 mm and an average wall thickness of 8 mm, sourced from The Energy Research Institute [20] were used to fabricate FRBC beams of of 4 × 5 culm matrix and length 2.1 m. The tensile and compressive strengths of this batch of bamboo culms were determined as 240 MPa and 31 MPa respectively and the moisture content ranged from 8 to 12%. The age of bamboo culms at the time of testing was about three years. This is less than the recommended age of three years as per IS 15912 [10]. However, it should be noted that at the time of testing (between 2011 and 2013), codal guidelines were not available. The beams were tested for structural adequacy and compliance of composite action using the experimental set up shown in Fig. 2(a). They were experimentally found to act as composite units until close to failure, with the strain distribution found linear throughout the depth of the beam right up to the point of failure (Fig. 2b). Typical load-deflection behaviour is shown in Fig. 2c. The beams reached the end of the elastic region at between 60 and 100 mm displacement, initiation of plastic behaviour indicated by the fact that the head of the jack continued to be extended but with no apparent increase in the load resistance, with corresponding peak loads lying between 70 to 100 kN. The beams themselves withstood ultimate applied moments between 39.4 and 52.5 kN-m. At ultimate load, the failure was found to be typically governed by the local crushing of the outermost bamboo culms radially at the supports and the crushing of the bamboo spreader under the loading points. The beams’ post peak behaviour displayed high ductility, something desirable for achieving the requisite seismic performance. Upon removal of the loads, the beams were found to almost return to their original shape. Neither major rupture in the bamboo culms nor inter-bamboo shearing failure were noticed visually, thereby displaying excellent recovery. Full details covering all three beams can be found in authors’ related publication [19].

Fig. 2
figure 2

Experimental validation of FRBC [19] (a) Experimental set up (b) Strain distribution across depth confirming composite action (c) Load–deflection behaviour

Full size image

Next, a procedure was devised to join straight FRBC elements using epoxycrete-steel rebar jointing, so as to obtain portal frame type construction, as illustrated in Fig. 3 [18]. Epoxycrete is a mixture of cement, fine and coarse aggregate and epoxy. Unlike concrete, epoxycrete can cure in 24 to 48 h, yielding high compressive strengths of over 40 MPa. This element to element joining approach paves way for rapid erection of large frame type structures using FRBC members, which could be manufactured in workshop to ensure superior quality and joined using steel rebars and epoxycrete rapidly at the site on industrial scale.

Fig. 3
figure 3

Epoxycrete based jointing system to obtain beam-column framing system based on FRBC

Full size image

After mastering FRBC and epoxycrete based jointing, three full-scale FRBC portal frames were fabricated at IIT Delhi and tested in collaborative mode at Trinity College, University of Dublin, Ireland, to evaluate behaviour and performance. In this article, only one of the three frames, subjected to largely horizontal load, is described for brevity, the readers may like to visit authors’ related publication [21] for full details of another frame, tested under combined vertical and horizontal loads. The FRBC beams and columns, of lengths 2.95 m and 2.4 m respectively, were fabricated separately and assembled together through the use of epoxycrete. The bamboo used for the fabrication conformed to the species Dendrocalamus strictus, while other materials included Araldite epoxy, polypropylene fibres, fine and coarse aggregate, steel bars (12 mm diameter) and steel wires of 1 mm diameter. The average size of the bamboo beam-column cross- section was 270 × 230 mm, with a 6 × 5 arrangement of the bamboo culms, whose average diameter was in the range of 38 to 43 mm and wall thickness 8–10 mm. All the joints, intended to be rigid, were cast monolithically. On each portal frame, 38 electrical strain gauges were installed on to the reinforcement in the joints and 58 strain on the bamboo culms at critical locations situated near the beam-column joints, at the middle of the beam and at the feet of the columns. The locations and labels for the strain gauges are shown in Fig. 4 in detail. The frames were tested on the 3000 kN capacity internal reaction frame at Trinity College, University of Dublin, Ireland. Linear variable displacement transducers (LVDTs) were used to measure the horizontal and the vertical displacements. For the frame described here, the horizontal load was gradually increased to 40 kN and maintained constant, followed by the application of the vertical load, whereupon the horizontal load was increased further, as shown in Fig. 5a. However, during this process, the vertical load jack underwent substantial lateral distortion (see Fig. 5a), forcing the test to be terminated just before the complete failure of the frame. Hence the applied loads were released prematurely. Thereafter, only a horizontal load was applied, with the intent of testing the frame under sway only. The load reached a maximum value of 65 kN. The displacement continued to be increased after reaching this peak load. Finally, when the displacement eventually reached 153 mm, the right end of the bamboo frame was found to be touching the main steel frame, hence reaching the maximum possible displacement in the set up. The test was therefore stopped at this stage. Cracking sounds were heard well before the final failure load was reached. A long crack was observed in the joint at this stage, as shown in Fig. 5b. In an actual structure, this might work as a warning to evacuate the building in case of an emergency. Epoxy bond failure between culms was also observed. On the removal of the loads, the frame members apparently regained their initial positions, which confirms extreme resilience of FRBC.

Fig. 4
figure 4

Dimensional and instrumentation details of FRBC frames [21]

Full size image
Fig. 5
figure 5

a FRBC frame under horizontal load during the test. b Crack in top left junction of frame

Full size image

Figure 6 shows the horizontal load vs horizontal displacement history of the frame. Apparently, the graph is shifted from the origin because the frame was already subjected to partial load (as mentioned above), due to which some residual displacements were observed in the frame after returning back to zero load. Points O, A, C and E represent the various stages during the test. Large inelastic deformation was observed from A to C, which points to failure of the frame. A small drop in the horizontal load between A to C can also be observed, possibly due to some delamination or local rupture of bamboo culms. The gap between E and O represents the residual displacement in the frame due to permanent deformation. Figure 7a, b and c respectively show the variation of the strain measured by gauges LB1, RB3 and RT1 with respect to the horizontal load (see Fig. 4 for strain gauge locations). For strain gauge LB1 (Fig. 7a), located on the outer face of the bottom of the left column, starting with some residual strain from previous loading, tensile strain rises with little additional strain during the inelastic phase. No major permanent locked-in-strain can be observed after the test, which implies that there was negligible plasticity at this location. The slope of the line C-E is the same as from O-A, indicating almost same modulus of elasticity on unloading. For strain gauge RB3 (Fig. 7b), located on the top of the right end of the beam (see Fig. 4) overall compressive strain can be observed in the graph. The load dropping between points A and C was possibly owing to internal delaminations. The continuing compressive strain from A to C indicates substantial inelastic behaviour culminating in large residual strain represented by EO. For strain gauge RT1 (Fig. 7c) located on the inner face of the top of right column (Fig. 4), the compressive strain from O to A is in accordance with the bending moment distribution. However, the absence of any significant compressive strain from A to C suggests no plastic behaviour here. This is further reflected in the very small residual strain EO when the load was removed. This suggests that this location was not active in the mechanism formation.

Fig. 6
figure 6

Load vs displacement behaviour of FRBC frame under horizontal load

Full size image
Fig. 7
figure 7

Horizontal load vs strain for strain gauges (see Fig. 4) (a) LB1 (b) RB3 (c) RT1

Full size image

After this and two more tests on FRBC portals [18, 21], it was revealed that the FRBC members were able to assimilate huge amounts of force and deformation combined. Tests revealed that all the frames displayed overall resilience in terms of capacity demonstrating that from structural performance considerations, FRBC is a competitive alternative to RC and steel for building construction with earthquake resistance capabilities. It established beyond doubt that the failure of an FRBC frame is not brittle as in RC frames. Hence, sufficient warning shall be available to the occupants.

Based on above comprehensive testing and analysis, a closed form expression based on linear elastic theory was formulated for estimating the peak moment of resistance of the FRBC beams. The formulations enable accurate determination of the neutral axis depth location substantiated by experimental observations. The expressions for moment capacity could be employed for estimating the allowable moment capacity of FRBC beams in real-life structural design. Authors' related publications [18, 21] may be referreed for details.

3 Battened bamboo system for secondary elements

FRBC elements covered in the previous section are suitable as the main elements of structural system, such a primary beams and columns of a frame system. For secondary members or elements subjected to low to medium forces and moments, light battened bamboo system (LBBS), comprising of four to eight bamboo culms, tied by battens at regular spacing, can be adopted. The spacing of the battens is maintained so as to ensure that overall slenderness ratio (of the resulting system) governs rather than the slenderness ratio of the individual culm, imparting it higher axial capacity. One such column, made from four bamboo culms, having cross-sectional dimensions 300 × 300 mm and height of 3 m, is shown in Fig. 8. Half split bamboo segments act as battens for this LBBS member at a spacing of 200 mm. Three such LBBS units, were tested for compression under compressive loads at Trinty college, University of Dublin, as shown in Fig. 9a. Figure 9b shows the load displacement curve of one of the LBBS column. After attaining a maximum load of 21 kN, the column displays a ductile behaviour at a reduced load of about 17 kN. Observing strain data measured at the four culms (not presented here) revealed initiation of bending in the top and the middle regions of the column. Full details of the tests can be accessed from the related publication [22]. These and other load tests demonstrated that LBBS elements are structurally suitable for resisting direct compression members of lightly loaded structures like sheds. However, LBBS elements were unable to perform as composite units when subjected to flexure [23]. This problem of inadequate flexural capacity of LBBS was addressed by means of a hybrid configuration obtained by integrating FRBC elements as bands in LBBS, so as to result a into an arrangement shown in Fig. 10. As can be seen from the figure, four equally spaced FRBC sections (seen as white bands) act as primary battens and steel rebars act as secondary battens. This configuration is called as hybrid FRBC-LBBS (HFL) system [24, 25]. Structural testing of this configuration, with dimensions 250 × 250 mm, and length 2 m, under flexure (see Fig. 11a) revealed perfect composite behaviour and adequate load capacity. Figure 11b shows typical load versus deflection pattern of one of the four test specimens and Fig. 11c strain vs deflection behaviour, displaying perfect composite action, with the top culms in compression and bottom culms in tension An average flexural capacity of 17 kN-m was found from multiple tests on HFL elements. Hence, HFL is experimentally found suitable for flexure in terms of composite action by four principal bamboo culms.

Fig. 8
figure 8

LBBS structural system for lightly loaded structures

Full size image
Fig. 9
figure 9

Full-scale testing of LBBS column under compression at Trinity College, University of Dublin (a) Column in test rig (b) Load vs deflection plot

Full size image
Fig. 10
figure 10

Achieving hybrid structural system by combining LBBS and FRBC

Full size image
Fig. 11
figure 11

a HFL beam under test (b) Load versus deflection behaviour (c) Strain vs load (top culm) (d) Strain vs load (bottom culm)

Full size image

4 Structural evaluation of cow-dung bricks

Malik [12] developed a technique for manufacturing bricks using cow-dung as the main constituent material. These brick are called as gaucrete (gau means cow in Sanskrit). Clay is used for stabilization and lime for cementitious effect. These bricks are unburnt and hence carry the tag of being emission free and zero embodied thermal energy. As compared to burnt clay bricks, the density of the cow-dung bricks is about 1000 kg/ m3, implying light-weight construction and invoking proportionally reduced earthquake forces. Hence, these bricks are ideal candidate for masonry infills for FRBC frames. Three such bricks, of dimension 110 × 80x225 mm, underwent compressive strength evaluation about four weeks post manufacture. The technical specifications of the bricks, including the mix proportion of constituent materials, are summarised in Table 1. On testing the gaucrete bricks in accordance with IS 3495–1 [26], it was found that their structural behaviour was much different from traditional burnt bricks. Figure 12a to d show typical stages undergone by one of the bricks prior to failure. Figure 12e shows the stress–strain plots of the three bricks. It can be observed that the stress–strain plot does not have distinct yield or ultimate stress point. This was correlated with experimental observations that the bricks continued to resist compressive stresses even after appearance of visible major cracks. As such, no ultimate or yield strength can be distinctly defined. Therefore, for this study, the ultimate strength is adopted as the compressive strength corresponding to 10% strain, which gives an average value of 1.12 MPa, which corresponded to Fig. 12c. It should be noted that this was short term strength achieved after about four weeks of fabrication. The constituent materials, namely cow-dung and lime, attain strength slowly. Hence, much higher strength is expected after nine to twelve months and tests shall again be conducted after reaching that period.

Table 1 Specifications of gaucrete brick [12]
Full size table
Fig. 12
figure 12

Compressive strength test of Gaucrete bricks (a) Before applying load (b) First crack (c) Intermediate loads (d) Near failure (e) Stress–strain plots of three specimens

Full size image

After individual brick testing, tests were conducted for masonry units fabricated using gaucrete bricks of size 340 × 150 × 140 mm supplied by Sara Construction Company, with same constitution as in Table 1. For testing action as masonry, two different units: one with cow-dung lime mortar (cow-dung: lime ratio equal to 10:1 by mass) and the other with cement mortar (cement: sand ratio equal to 1:4), were prepared as shown in Fig. 13. Both had dimensions 700 × 600x140 mm. Figure 14 shows the load versus deflection curve for the two specimens. The masonry unit with cement mortar has exhibited close to two times higher failure stress as compared the masonry unit with gaucrete mortar. This is, however, the short term strength after about two weeks of casting. Tests shall be repeated again after six to twelve months for long-term assessment and published elsewhere.

Fig. 13
figure 13

Gaucrete masonry unit under vertical load test (a) System with cow-dung lime mortar (b) System with cement mortar

Full size image
Fig. 14
figure 14

Load versus deflection response of masonry units under vertical loads

Full size image

5 Fabrication of prototype modular dwelling unit using frbc frames and cow-dung masonry infills

After structural evaluation of FRBC beams and frames and cow-dung bricks in the laboratory, the authors carried the structural analysis, design and fabrication of a full-scale 3D prototype FRBC modular hexagonal unit as a proof-of-concept demonstration of the technology. This was achieved as part of a research and development project under Impacting Research and Innovation and Technology (IMPRINT), an initiative of the of the Ministry of Education, and operational under Science and Engineering Research Board (SERB), Department of Science and Technology, Government of India [27]. The objective of the sponsored project was to raise the technology readiness level of the FRBC technology to level nine and carry out proof of demonstration in the field. The project involved the conceptual design, detailed engineering calculations, and the fabrication of a modular structural unit, hexagonal shape (each side measuring 3 m in plan), resulting in a floor area measuring 23.38 m2 (251 ft2). Figure 15 illustrates the sequence of construction of the 3D FRBC frame from above the RC plinth beam, measuring 300 × 500 mm in size. The foundation system consisted of six isolated footings, of size 1 × 1x 0.3 m, concrete grade M 25 as per IS 456 [28], located 1 m below the existing ground level (allowable net bearing pressure was 150 kN/m2) and designed to withstand a load of two storeys, including the corresponding seismic/ wind loads [29, 30]. RC columns, measuring 300 × 300 mm, projected up from the foundations and were tied by the plinth beam. The FRBC elements measured 225 × 300 mm in size, and consisted of a matrix of 5 × 6 bamboo culms of Dendrocalamus strictus, with an average wall thickness of 8 mm. The dimensions were worked out after detailed structural analysis and design, including for seismic forces as per Zone IV of IS 1893 I [29] and wind analysis as per IS 875 III [30], with factor of safety of three for FRBC elements. The construction demonstrates that factory made FRBC elements can be assembled at site within a short time on lines of pre-engineered steel structure technology. It should be noted that such a hexagonal unit is expandable in nature [18] both horizontally as well as vertically owing to its special modular design. Though only a single storey structure has been constructed at site, the proportioning of foundations and members has been done so as to withstand loads, including wind and earthquake forces, corresponding to a two-storey construction [24].

Fig. 15
figure 15

Fabrication of model FRBC dwelling unit at IIT Delhi as part of IMPRINT II project (a) FRBC elements transported at site (b) Foundations and columns (c) Installation of beams (d) Full 3D FRBC frame after installation of member components

Full size image

The HFL configuration was considered for six inclined roof members spanning between the top end of the column and the central crown of the prototype structure, as shown in Fig. 16. The HFL elements are supposed to support a light-weight roof and resist local wind effects. For ascertaining the adequacy of the HFL roof beam for wind loads, the Indian design code IS 875: Part III [30] was followed, taking into consideration the basic wind speed, zone factor and other, risk coefficient, terrain and topography factors of Delhi. Detailed wind analysis of the structure revealed that the proposed configuration of HFL elements is structurally adequate for resisting wind loads. Post structural analysis, the maximum bending moment in HFL roof beams was computed as 5.7 kNm, against the average ultimate load capacity of 17 kNm obtained by experimental testing [25]. Hence, a factor of safety greater than three has been achieved. Maximum bending moment induced in the HFL from seismic loads was found to be 0.5 kNm, which means the main hexagonal frame system shall predominantly resist the earthquake induced loads owing to its much larger stiffness. After analysis and design, fabrication and integration of the roof HFL elements on the top of the hexagonal structure was achieved using epoxycrete joints, with steel rebars used as reinforcement, as shown in Fig. 16a to f.

Fig. 16
figure 16

Phase wise integration of inclined roof beams. a Joint prior to addition of HFL. b Placement of HFL members. c Joint at crown. d Preparation of epoxycrete. e Casting process. f Final joint after setting of epoxycrete

Full size image

Figure 17 shows the phase wise construction of the cow-dung masonry infills. Four walls were constructed using cow-dung lime mortar and two using cement sand mortar. Figure 18 shows the final structure constructed on ground. Minor cracking was observed on the masonry built using cow-dung mortar after one month owing to shrinkage. Regular observations are being made to study long-term performance of both the mortar types. The fabrication of the complete structural system demonstrates feasibility of sustainable construction using bamboo and cow-dung bricks.

Fig. 17
figure 17

Phase wise construction of masonry infills. a Bare FRBC frame. b Gaucrete masonry erection. c A view of gaucrete masonry using cow-dung lime mortar. d Front view. e A view of gaucrete masonry using cement mortar. a View after erection of all walls

Full size image
Fig. 18
figure 18

Final constructed structure (a) An artist's impression (b) Actual structure

Full size image

6 Conclusions

This paper has presented the development and practical demonstration of alternate green technology for a achieving a built environment suitable for urban as well as rural landscapes. A prototype unit, measuring 23.38 m2 (251 ft2) has been constructed as a demonstrative modular unit. The main beams and columns have been constructed using FRBC elements. The secondary inclined roof beams have been fabricated using HFL elements and the masonry infills constructed using cow-dung based Gaucrete bricks, rendering an overall carbon negative approach to construction.

All the structural members were proportioned after detailed structural analysis as per Indian standard codes of practice, including wind and earthquake, and all the members were proportioned to achieve a minimum factor of safety of three. The use of epoxycrete for real-life joints was also successfully demonstrated on the prototype. It provides an alternative to concrete for using a waterless beam-column joint that becomes fully effective within first 48 h of casting. It should however be noted that minimal quantities of polypropylene fibres and epoxy adhesive, which are non-biodegradable, have inadvertently been used for achieving FRBC. Studies are underway to effectively replace the epoxy adhesive by polylactic acid based bio-degradeable adhesive and polypropylene fibres by natural fibres and outcomes shall be soon published.

The Gaucrete bricks proved to be an ideal light weight and ecofriendly materials. Testing Gaucrete bricks and Gaucrete walls with two different mortars, namely cow-dung lime mortar and cement-based mortar were tested. Cement based mortar was found to impart higher overall strength in short term while long term evaluation shall be conducted after nine to twelve months. Being unburnt, the Gaucrete bricks are the zero CO2 emission construction material. The gaucrete masonry infills is expected to result in better thermal insulation as compared to burnt clay brick, studies are currently underway and outcomes shall be published elsewhere.

The prototype modular unit shall be continuously examined over next two years to study the performance of the alternate green materials used in the construction process. The design and construction has been done to achieve a hassle-free but technically sound structure that can be replicated easily using the local resources and manpower. Regions with limited resources or a high-temperature zone can easily adopt this construction practice. This will additionally provide more job opportunities in the field of construction using natural resources. Also, it will promote increased bamboo and cow-dung production in the agriculture and dairy industries. The economic worth of bamboo and cow-dung is expected to rise as engineers embrace them for construction, leading to increased demand and improved financial prospects for small farmers.