Fire Technology Ó 2015 Springer Science+Business Media New York. Manufactured in The United States DOI: 10.1007/s10694-015-0504-z
Fire Performance of Sustainable Recycled Concrete Aggregates: Mechanical Properties at Elevated Temperatures and Current Research Needs John Gales* , Carleton University, 3432 Mackenzie, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada Thomas Parker, University of Edinburgh, The King’s Buildings, Mayfield Road, Edinburgh EH9 3JL, UK Duncan Cree, University of Saskatchewan, Saskatoon, SK S7N 5A2, Canada Mark Green, Queen’s University, Kingston, ON K7L 3N6, Canada Received: 31 October 2014/Accepted: 18 May 2015
Abstract. The materials used for the construction of buildings are changing. There are now many sustainability drivers for developing novel green construction materials. An emerging material used for building construction is concrete with conventional coarse aggregates substituted as recycled concrete aggregates (RCA). This is a form of sustainable concrete. A finite number of buildings (>10) with this material have been constructed in North America, Europe and Asia. However; to help facilitate wide spread use and development of sustainable concrete with RCA, there is purpose in considering this material’s at-elevated temperature (in-fire) mechanical properties. To date, this topic has seen limited research attention as it is difficult to study. The study herein considered the mechanical properties of conventional and sustainable concrete with RCA. The only difference between the conventional and the sustainable concrete mixes was the mass proportion of a conventional natural coarse aggregate, Limestone, which had been substituted with coarse RCA (at replacement proportions of 0%, 30% and 100%). Both the ambient and elevated temperature mechanical properties were considered with compressive mechanical tests using an innovative optical technology for strain measurement. Based on the analysis performed, a proportional decrease in retained strength and elasticity of concrete at-elevated temperature with increasing RCA content was observed. For example both mechanical properties showed a 0.2% decrease in retained value for every 1% RCA increase at 500°C. In addition the modelling parameter of Poisson ratio appeared to be influenced by the heat imposed and the aggregate type contained within the concrete. For example at 500°C, this parameter showed an 73% increase for concrete samples with only Limestone aggregate and a 15% decrease for samples with only RCA (of mixed origin primarily Siliceous). This paper concludes with highlighting current knowledge gaps and research needs that when addressed could help improve the facilitation of using sustainable concrete’s with RCA in construction of buildings.
* Correspondence should be addressed to: John Gales, E-mail:
[email protected]
1
Fire Technology 2015 Keywords: Sustainable concrete, Recycled concrete aggregates, Material testing, Scanning electron microscopy, Digital image correlation, Mechanical properties, RCA
1. Introduction Fifteen years ago Jack Watts, the former editor of Fire Technology, wrote: ‘‘Sustainability is not a fad of the coming decade but an emerging tenant of excellence’’ [1]. Today, sustainability is an international initiative driving the choice of materials for various iconic buildings. LEED, BREEAM and other global certification bodies are helping to facilitate innovative and green construction materials. Meeting these certifications can be considered challenging when concrete is used due to concrete’s high embodied energy demand. For at least the last decade, various buildings have used a particular sustainable and novel concrete mix to help achieve green certification. This concrete blend was made by substituting conventional natural coarse aggregates with recycled concrete aggregates (RCA). RCA can be sourced and graded from demolition concrete waste. Figure 1 illustrates an example of coarse RCA. This novel construction material has been applied in real building construction as seen in Asia, Europe and North America (see Table 1 for an arbitrary selection of at least ten different buildings using sustainable concrete with RCA [2–11]). Public protection is important when any new material is used for buildings. The study of a new material’s behaviour to a fire can be part of this protection. Consideration of a material’s mechanical properties in fire can also help further develop, build confidence and facilitate the use of novel materials in the construction industry. In countries that use objective and performance based fire codes, it can be argued that new construction materials should show an equivalent structural response in-fire that traditional counterpart materials can demonstrate [12]. For example the time of failure could be compared between the two construction
Figure 1.
RCA as sourced.
Fire Performance of Sustainable Recycled Concrete Aggregates Table 1
Sustainable Concrete with RCA Building Applications Building Wessex water 60 Leicester Council house 2 Workplace 6 Enterprise park Samwoh research Middlehaven J-Cube Athletes village Okanagan
Country
Coarse RCA (%)
Date
Floors
Usage
Reference
UK Australia Australia Australia USA Singapore UK Singapore UK Canada
40 60 NR 20 NR 100 50 50 20 to 50 NR
2001 2004 2006 2008 2008 2010 2011 2012 2012 2013
2 4 10 4 3 3 10 6 10 1
Commercial Commercial Residential Commercial Industrial Industrial Residential Commercial Residential Residential
[2, 9] [3] [4] [2] [5] [6] [2] [7] [2, 10] [8, 11]
NR specified, yet not reported
materials (new and traditional) with a full-scale fire test. Providing the novel material demonstrates at least the same performance in comparison to its more traditional counterpart, the new construction material can then be considered an alternative material (or design solution). With concrete being well known to display mechanical property differences to fire when aggregates are changed [13], it is natural to expect a mechanical property differences for sustainable concretes with RCA in a fire. However, prior to performing expensive full-scale fire testing, there is practicality to consider the mechanical properties of these novel sustainable concrete materials first to fire at a smaller scale. To date sustainable concrete with coarse RCA has received limited attention for mechanical properties post-fire (heated, cooled, and then loaded at-ambient temperature) as was provided in a recent review of recycled materials for use in concrete [14]. For example, an earlier work [15] studied the residual compression strength of concrete prepared with natural coarse granite aggregates and concrete containing 75% by volume of coarse RCA. The samples were heated to 500°C and soaked for 1 and 4 h followed by a slow oven cooling to room temperature. Compared to the non-heated control specimens, after 1 h the conventional and RCA concretes decreased in residual strength by 16% and 10% respectively. After 4 h of heating, both concretes residual strength were reduced by approximately 26%. Those authors suggested improved performance of RCA concrete was due to the interface between the old cement on the RCA and the new cement-interfacial transition zone. Micro and macro cracks in the mortar were thought to be reduced due to the similar coefficient of thermal expansions. The mortar quantity in RCA concrete tends to be elevated. For this reason, a study [16] examined the effect of increasing the mortar content by varying the w/c ratio from 0.4 to 0.7. The authors concluded coarse RCA concretes with a low w/c ratio performed better in residual compressive strength than conventional concretes when they were exposed to high temperatures. Another study [17] investigated the replacement of siliceous coarse aggregates with coarse RCA from a demolished airport runway. RCA replacement amounts ranged from 0% to 100%. The specimens were heated
Fire Technology 2015 from 200°C to 800°C and held for 2 h followed by cooling to room temperature. For 30% RCA replacements, the residual compressive strength were lower than the control. For replacement ratios greater than 50% and between 400°C to 700°C, the concrete containing RCA had a higher residual compressive strength than the conventional concrete. However no further reasoning was given to explain this trend. In a similar study [18] conventional coarse limestone aggregate concrete was replaced with coarse RCA limestone in the amounts of 0% to 100%. The specimens were exposed to temperatures of 400°C to 800°C for 1 h and cooled to room temperature. The residual compressive strengths decreased by 20%, 25% and 40% after exposure to 400°C, 600°C and 800°C for both conventional and RCA concretes. A relationship was not observed between the degradation of residual mechanical properties and the replacement rates of natural coarse aggregates by RCA. A more recent work [19], reviewed the use of RCA from curbs and sidewalks as a partial replacement to coarse limestone aggregates. The conventional aggregates were replaced with 0% to 100% RCA. The samples were heated from 250°C to 750°C and held for 1 h at temperature before cooling to ambient temperature. The results determined when 50% or more of RCA was added, the residual strengths of RCA concrete were higher than those of normal concrete. The studies conducted on the residual elevated temperature strengths of RCA showed a high replacement percentage of RCA could be beneficial and equal or greater in residual strengths as compared to the conventional concrete. However, the difficulty to study the life critical in-fire performance (heat and load at-elevated temperature) has received little to no attention to the awareness of the authors. Even though conventional normal and high strength concretes are relatively established materials, many researchers noted test data in the hot conditions were not common [20–24]. The hot compression strengths are equally important to evaluate as the concrete must maintain its compressive hot strength throughout the duration of a fire. The literature indicates a lack of knowledge about the elevated temperature effect of substituting conventional aggregates with RCA in the fabrication of structural concrete. This paper aims to study the in-fire, rather defined at-elevated temperature, mechanical properties of sustainable concrete containing RCA. This study is in an effort to help develop, instil confidence and facilitate the further use of this novel sustainable material technology for application in the construction of future structures.
2. Background and Objectives Recent literature reviews [13, 25, 26] on concrete mechanical properties for at-elevated temperature behaviour have highlighted difficulties with comparing various researchers’ data sets. This is due to the use of different curing conditions [13, 25], heating rate [13, 25, 26], loading rates [25], and the shape [25, 26] of concrete among various researchers’ test programs. These all affect the mechanical properties of concrete at-elevated temperatures. To compare different concrete mix’s mechanical properties at high temperature, there can be desire for new studies to
Fire Performance of Sustainable Recycled Concrete Aggregates consider their own control concrete mixes for at-elevated temperature mechanical testing. Additionally, while there have been international movements to provide guidance for at-elevated temperature mechanical material testing of concrete (RILEM for example [27]) there are still specific testing challenges with obtaining deformation data of concrete in mechanical tests. For example, brittle material failure can damage instrumentation and heating furnaces, therefore minimizing equipment damage is a desirable experimental approach. The above issues were kept in mind for the current investigation. To study the effect of RCA aggregate substitutions with at-elevated temperature mechanical uniaxial compression tests, the authors cast three different concrete mixes. The mix designs considered concrete with conventional natural aggregates as a control. The other two mixes specified a proportion of the conventional natural aggregate to be substituted with RCA. The study presented herein considered the mechanical properties for each mix (ultimate stress—f 0 c (MPa), approximate stiffness at 40% ultimate stress—E (MPa), and strain at ultimate stress—ec). Both the at-elevated and ambient temperature conditions were considered and compared. In practice it is common to have defined modulus elasticity as taking the secant modulus at 40% ultimate stress from the experimental stress strain curve. A source publication which promotes this practice is ASTM C469-14 [28]. To minimize equipment damage all deformation was approximated using a novel non-contact and optical deformation measurement technique called digital image correlation (DIC). Additional parameters which are required for modelling concrete in fire were also considered for study such as thermal expansion—et and Poisson ratio—v. Concrete samples were tested in uniaxial compression at both ambient and elevated temperatures. This was achieved using an Instron 600LX servo-hydraulic materials testing frame. The frame was equipped with a furnace and a quartz glass specimen viewing window (see Figure 2). Deformation was approximated using the DIC technique. A post-test investigation was carried out using a MLA 650 FEG environmental scanning electron microscope (SEM) to help explain observed results. The tests were performed with the following objectives: to examine the use of a novel measurement procedure for obtaining mechanical properties of concrete at-elevated temperature that will not damage equipment; to compare the mechanical properties of sustainable concretes with RCA to conventional concrete at-elevated temperatures; and to consider novel modelling insights into the performance of concrete in-fire.
3. Experimental Methodology Each concrete batch used the same volumetric mix design with target cube strength of 40 MPa. All concrete batches were specified with the same quantities of water, ordinary Portland cement content; fine aggregate; and graded coarse aggregate to a maximum size of 10 mm. The only difference between the conven-
Fire Technology 2015
Figure 2. Compression test experimental set up using DIC with gauge length patch shown in red (Color figure online).
tional and the sustainable concrete mixes was the mass proportion of a conventional natural coarse aggregate, Limestone, which had been substituted with coarse RCA (at proportions of 0%, 30% and 100%). Limestone is a common natural aggregate and therefore was specified. Each mix was compared to allow the effect of RCA additions to be rationally understood. The proportion of RCA was chosen on the following basis: 0% RCA—the conventional concrete with pure Limestone aggregate. This mix was meant as the control; 30% RCA—when no other changes to the mix design were made, the mechanical effects of RCA substitution up to 30% were accepted to be relatively small (see [29–31]); and 100% RCA—pure RCA substitution as coarse aggregate was defined to represent an extreme condition of aggregate substitution as can be seen in real construction. The sustainable concretes used RCA sourced from a structure that contained mixed gravel as its coarse aggregate. The RCA was crushed and graded from a 20 month old lab scale post-tensioned concrete slab which had been slated for construction and demolition waste disposal. This was considered a good green initiative of reducing research waste. The coarse RCA was sourced from visually undamaged locations of the concrete slab system. The slab was of 50 MPa cube strength (tested at demolition) and its concrete was made with mixed gravel aggre-
Fire Performance of Sustainable Recycled Concrete Aggregates gate which (identified during casting) contained Limestone aggregate, but also contained Quartz; Silica; Ferro-magnesium; Olivine; Sandstone; Mica; Feldspar; Orthoclase; and Jasper aggregates. The RCA contained siliceous and calcareous aggregates. Examining the mix design of the RCA source identified specifications for the addition of supplementary ground granulated blast furnace slag (GGBFS) at 50% cement replacement. The RCA source is clearly distinctive. Selected concrete mix and aggregate properties are tabulated in Tables 2 and 3, respectively. Figure 1 illustrates the raw RCA aggregate before casting. Casting of all concrete specimens took place in the United Kingdom. Due to availability of specialized equipment, mechanical uniaxial compression tests reported herein were conducted in Canada. Since the samples had to be shipped internationally, the specimens were not cast with embedded thermocouples as this would have restricted shipping. The lack of embedded thermocouples has implications which will be discussed. The number of specimens cast was limited to the volume of the onsite concrete mixer in the United Kingdom. A minimum of four large cubes (100 9 100 9 100 mm3) and one small cube (20 9 20 9 20 mm3) were cast for each concrete mix. The benefit of casting one batch for each mix was the variability in added materials (water, aggregates, cement, etc.) between fabricating each batch is removed. As will be observed, key mechanical property data pairs (f 0 c, E) exhibited small coefficients of variation (500 20 20 500 500 >500 20 20 500 500 560 >500
f 0c (MPa) E (MPa)
Test type Ambient strength Ambient strength Ambient strength Elevated temperature Elevated temperature Unloaded but heated Ambient strength Ambient strength Elevated temperature Elevated temperature Unloaded but heated Ambient strength Ambient strength Elevated temperature Elevated temperature Elevated temperature Unloaded but heated
strength strength
strength strength
strength strength strength
43.3 43.4 44.0 40.0 39.8 – 45.1 47.2 38.2 39.6 – 48.7 47.7 34.6 35.5 31.3 –
21,100 23,800 22,000 9400 10,800 – 21,000 22,700 7300 7200 – 19,300 24,400 5500 5000 5300 –
v
ec
et (°C)
0.16 0.25 0.17 0.31 0.36 – 0.23 0.17 0.28 0.25 – 0.19 0.21 0.19 0.15 0.13 –
0.004 0.006 0.008 0.010 0.011 – 0.004 0.004 0.014 0.014 – 0.005 0.003 0.016 0.012 0.014 –
– – – 7.3E-06 4.9E-06 – – – 6.9E-06 6.8E-06 – – – 8.1E-06 7.0E-06 7.3E-06 –
one cube at four different temperatures (see Ref. [27] for discussion that recommends at least two tests per temperature). An additional 100% RCA concrete cube specimen was tested at 560°C to consider the possible elevated temperature effect on some material properties. For all uniaxial compression tests reported herein, the concrete cubes were placed between two steel platens to distribute loading equally. Each cube, under actuator maintained zero applied stress, was then heated with a furnace control heating rate of 2°C/min to the target temperature. This temperature was then held for a minimum of 2 h. This gave a total heating time of 6 h. For safety reasons, a slower heating rate was not used as this would have extended the duration of the tests beyond the normal safe operational hours of the laboratory. A variety of heating rates can be found in literature. Most available guidance implies a temperature heating rate for accidental (fire) conditions below 2°C/min and cautions of concrete spalling [27]. Some recent testing by other high temperature sustainable concrete studies have also used a rate of 2°C/min [36]. Furnace temperatures were monitored with several K-type thermocouples with typical accuracy of ±2.2°C. During the soak phase, negligible thermal expansion of the concrete was observed (by stroke measurement) within the first 15 min of soaking. To assess the suitability of this heating regime while also defending the use of no internal thermocouples at cube centre, separate tests were performed by the authors using the same heating procedure but using slightly larger concrete specimens (approximately at twice the size in volume). These heating tests were performed with K-type thermocouples embedded at the centremost portions of their specimens. This paper’s
Fire Technology 2015 authors found that a soak time of 2 h was satisfactory to ensure the centre of the specimen was within range of the target temperature of the furnace.
3.2. Loading All compressive tests (high temperature and ambient) were controlled in loading using stroke at 0.5 mm/min rather than a stress control (MPa/s). Stroke control permitted the authors to stop any test safely after peak stress was observed. Stress rate control was not used as there was a high risk of debris impact at specimen failure which could damage the furnace’s viewing window. Testing beyond the peak load can have violent failure that could occur within the furnace. Useful post-peak softening data for modelling and final failure patterns were therefore sacrificed in an effort to prevent equipment damage; however, other relevant mechanical parameters could still be obtained. The stroke rate utilised for defining material properties was sufficient in order to induce the minimum stressing rate (0.15 MPa/s) in compliance with ambient North American testing standards for hydraulically operated loading actuators [33]. The authors note that available studies which have used stroke control tests indicate that a variety of values, including 0.5 mm/min [37], have been used by other researchers to test concrete at high temperature [34, 37].
3.3. Deformation Measurement At-elevated temperature, deformation based properties are challenging to measure accurately using conventional technologies and instrumentation (due to concrete’s brittle failure). Therefore a bespoke non-contact optical DIC technique was used herein to approximate a material deformation (strain). DIC is a technique capable of measuring deformation optically by comparing a sequence of high resolution digital images using a post-processor image processing (pixel subset tracking) algorithm. DIC was performed by using a digital single lens reflex (SLR) camera. This study used a Canon EOS 5D camera acquiring images at defined rates of 1 Hz during loading (1 image per second), and 0.03 Hz (1 image every 30 s) during heating through the furnace specimen viewing window. The post-processing GeoPIV8 image correlation algorithm [38] was used to translate image pixel subset movement into deformation measurement. The samples needed to be flat (cubes) as a curved surface (cylinders) would be partially out of plane prohibiting this measurement technique for measuring accurately transverse strains. To help the GeoPIV8 software interpret deformation, most samples were coated on one flat face with high temperature black paint and speckled with high temperature white paint to create a non-uniform texture that is optimal for GeoPIV8 tracking. These paint mixtures were chosen to be similar to those that had been utilised in other high temperature tests [39]. Previously the DIC technique has been successful in tracking strain and deformation of concrete at ambient temperatures as was described within: [40–43]. At high temperature, DIC has been shown to accurately describe the deformation behaviour of various structural materials and assemblies (see [39, 44, 45]).
Fire Performance of Sustainable Recycled Concrete Aggregates While technique procedures can be found within the above references, in brevity the procedure to approximate deformation and strain from imaging is summarized as follows: 1. user defined square pixel subsets are overlaid onto the initial reference image using software; 2. the images are sequenced in order and the post-processor software activated; 3. the difference measurement between these pixel subsets from the reference image to the later image in pixels is calculated; and 4. using the output pixel values, strain and/or unique deformations are calculated and determined.
3.4. Micro-scale Analysis The use of SEM can help explain what micro-scale cracking mechanisms may be contributing to mechanical property changes at elevated temperature for each concrete mix. The technology can be used to investigate the presence (or absence) of micro-cracking patterns after various controlled heating and loading conditions. SEM imaging analysis was conducted on sample units from virgin (un-cast) coarse RCA (10 mm), heated and unheated failed concrete cubes (cut to size 20 9 20 9 20 mm3) and aforementioned samples from heated but unloaded concrete (also sized to 20 9 20 9 20 mm3). Samples were cut and prepared using a water cooled diamond blade. The originally unheated samples did not exhibit any discoloration after cutting (see [46] for discussion on concrete colour change which can indicate high heat exposure). Therefore it is assumed that the cuts did not impart significant heat to the samples. SEM images of each sample were taken at regions of interest (specifically the aggregate-cement interfaces) at varied micro-metre resolutions. Copper tape which displays brighter than the concrete in SEM imaging was utilised to point to regions of interest. The utilised SEM also had functionality to undertake chemical analysis. This function was performed to help identify RCA (since some the RCA was not limestone).
4. Results The results of the current study are broken into three sections corresponding to the paper’s objectives. The first section verifies the use of the non-contact and optical DIC procedure to measure deformation. With an adequate approximation capability, a comparison of the mechanical properties (ambient and at-elevated temperature) of sustainable concretes with RCA to conventional concrete is then presented. Selected results of E, f 0 c, and ec are provided and all relevant results are also tabulated in Table 4. In this section SEM results are described to help explain the observed properties of all concrete mixes. The section concludes with a generalized discussion on modelling parameters useful for concrete behaviour in-
Fire Technology 2015 fire. Novel insights relating to thermal expansion properties of the mixes and their Poisson effect are provided.
4.1. Verification of DIC Technique for Deformation Approximation The optical DIC technology was used to measure both transverse and longitudinal strains. Figure 2 illustrates the experimental set-up and the default compressive strain measurement location and pixel subsets for each compressive test. Transverse strains were calculated in the perpendicular direction at mid-height of the cube (not shown in Figure 2 for clarity). The default strain gauge length in all cases was taken as 1500 pixels (75 mm length). Measurement scatter with this length was shown to be less than 0.005% strain [39]. Gauge lengths above 1000 pixels were appropriate for reducing the influence of the inherent bias error of the DIC technique (see [43]). The gauge length size represented the validated high end for uniaxial at-elevated temperature testing of materials [39]. A pixel subset of 64 9 64 pixels was followed as was defined as appropriate for concrete within Ref. [41]. In order to verify the DIC technique’s applicability for approximating deformation in uniaxial compression tests, a compressive test on a conventional concrete cube at ambient temperature was performed (Figure 3). Measured DIC strain was compared to that recorded by a 120 X strain gauge. Maximum deviation between these methods was less than 0.05% strain. The 120 X strain gauge stopped functioning just prior to failure and below 1% strain. Since the DIC measurement matched satisfactorily to the strain gauge reading, the dilation of the concrete towards the camera (out of plane movement) was assumed to be negligible.
Figure 3. Comparison of measured strain at ambient temperature between a strain gauge and DIC.
Fire Performance of Sustainable Recycled Concrete Aggregates An additional rigid body test used to assess lens distortion, showed that effect negligible at extreme ends of the sample. A verification exercise was also performed by comparing the difference in measured deformation rate between the actuator cross head movement (0.5 mm/min) and the DIC measured extension rate at both elevated and ambient temperature. The differences in crosshead rate measured by the DIC technique were found to be at maximum 4% different (see Figure 4). Efforts were made to reduce the levels of measurement error by considering the best practices listed in aforementioned literature [39, 41, 43]. However, with the unique nature of high temperature testing of concrete and the risks associated with instrumentation breakage while testing, a rigorous endeavour to quantify error at high temperature may benefit future studies that use the DIC technology. As will be seen in Sect. 4.2 the deformations as measured by this DIC technique for the baseline concrete mix followed conventional uniaxial concrete mechanical properties at high temperature (ultimate strain level at peak load, stiffness reductions at high temperature, increase in strain with high temperature in comparison to ambient results, etc.). Therefore the authors advise results measured with DIC can be used with confidence, based on this verification study and the experiences of other authors described herein.
Figure 4. Differences in actuator DIC measured extension at ambient and 500°C.
Fire Technology 2015
4.2. Comparison of the Mechanical Performance of Sustainable Concretes with RCA to Conventional Concrete This section begins with material comparison at ambient temperature, followed by a discussion to compare between elevated temperatures. SEM results are then used to explain the mechanical properties observed. 4.2.1. Ambient Temperature Mechanical Properties At ambient temperature, compressive tests showed an f 0 c increase in the sustainable concrete as the proportion of RCA coarse aggregate increased (Figure 5). This trend may have been influenced by the concrete strength (about 50 MPa) of the source material used for obtaining the RCA coarse aggregate. This strength was greater than the specified mix design. Other researchers have seen similar behaviour [47–49]. In addition to the old concrete strength of the source RCA, another effect contributing to this phenomenon, could be the more optimal curing conditions present from higher retained moisture in the RCA used (5% mass moisture of RCA alone). Kou and Poon [49] recently observed in an extensive test series that same strength gain behaviour, which those authors attributed the water entrained by the RCA, could have contributed to the growth and formation of additional Calcium Silica Hydrate in the capillary pores within the aggregate. They noted that these pores can then be made smaller (by refinement, filling and transformation of the RCA) which could lead to an improved compressive strength. For the ambient tests, there was less than 1.5 MPa variability observed with respect to f 0 c for each mix. However, tests showed considerable variability between measured ec and E (Figures 6, 7, respectively) for each mix. No clear
Figure 5.
f0 c with increasing RCA.
Fire Performance of Sustainable Recycled Concrete Aggregates
Figure 6.
E with increasing RCA.
Figure 7.
ec with increasing RCA.
trends or obvious differences could be observed in either parameter as RCA content increased. The variability observed in E at ambient temperature (as taken by the secant modulus) was due to inherent measurement scatter errors present in the DIC measurement technique which measured very small strains (
