This study presents the hydration reactivity and alkali silica reaction (ASR) of ultrahigh strength concrete (UHSC) that has been made more sustainable by using spent foundry sand. Spent foundry sand not only is sustainable but has supplementary cementitious material (SCM) characteristics. Two series of UHSC mixtures were prepared using a nonreactive and reactive sand (in terms of ASR) to investigate both the impact of a more reactive aggregate and the use of spent foundry sand. Conduction calorimetry was used to monitor the heat of hydration maintained under isothermal conditions, while ASR was investigated using the accelerated mortar bar test (AMBT). Additionally, the compressive strengths were measured for both series of mixtures at 7, 14, and 28 days to confirm high strength requirements. The compressive strengths ranged from 85 MPa (12,345 psi) to 181.78 MPa (26,365 psi). This result demonstrates that a UHSC mixture was produced. The calorimetry results revealed a slight acceleration in the heat of hydration flow curve compared to the control from both aggregates indicating increased hydration reactivity from the addition of foundry waste. The combination of foundry sand and reactive sand was found to increase ASR reactivity with increasing additions of foundry sand up to 30% replacement.
The challenges facing the concrete industry in the 21st century are greater than ever due to familiar problems such as various durability issues plaguing our infrastructure and their associated life-cycle impacts. These issues, coupled with increasing stringent environmental regulations, have resulted in the need of a sustainable ultrahigh strength concrete (UHSC) that can achieve the goal of safer, durable, and more environmentally-friendly infrastructure. For instance, more effective utilization of locally available industrial wastes/byproducts in concrete such as foundry sand, fly ash, and slag can impart enhanced fresh and hardened properties to concrete, while significantly reducing the disposal volume of these materials. Given the fact that concrete is the most widely used man-made building material in the world, there is an opportunity for significant economical savings and environmental benefits from increased incorporation of waste material in concrete.
The American Concrete Institute (ACI) has defined UHSC as a concrete meeting high strength that cannot always be achieved routinely, using conventional constituents and normal mixing, placing, and curing practice [
Spent foundry sand (FS) is a by-product of ferrous and nonferrous metal casting industries primarily consisting of high quality silica sand with uniform physical characteristics. Approximately 6–10 million tons of this waste is produced annually by the foundry industry in the U.S. alone. Spent foundry sand, when used as partial replacement of fine aggregate in concrete, has been shown to improve the mechanical properties of concrete [
Alkali silica reaction (ASR) has been one of the most destructive distress mechanisms dominating our infrastructure for several decades. The reaction occurs due to the high pH of the concrete pore solution as a result of the alkalis from the cementitious material. This aggressive solution attacks certain siliceous minerals found in coarse and fine aggregates that may result in a hydrophilic gel that absorbs water causing abnormal expansion. This expansion can lead to excessive cracking, often resulting in a reduction in the service life of affected structures. Since FS is highly siliceous, ASR expansion can be accelerated from the addition of FS in the mixture.
In the present research, multiple UHSC mixtures with locally available foundry sand were produced and analyzed for their hydration and alkali silica reactivity. Two control UHSC mixtures were developed based on a literature survey and bench line strength. One control used manufactured sand as the sole aggregate, which is a commonly used fine aggregate and typically not reactive (in terms of ASR). In order to assess the impact of foundry waste on the reactivity sequestration of UHSC mixtures, a second control mixture was developed that consisted of reactive sand as the sole aggregate. Foundry sand was then used to partially replace the fine aggregate in the control mixtures in 10, 20, and 30% by volume increments and their strength, hydration, and ASR performance were compared to the control values.
UHSC, like conventional concrete, can have a broad range of designs. Most UHSC are being designed without coarse aggregate, or coarse aggregate that is ≤9.5-mm (0.375-in.) [
In recent years, there has been extensive research conducted to study the effect of FS in concrete production. Fiore and Zanetti [
Ganesh Prabhu et al. [
Siddique et al. [
Mohammed Viquaruddin and Abdullah Mohammed [
A single ASTM C150 [
Chemical and mineral composition of cement and silica fume.
Compound | Cement | Silica fume |
---|---|---|
SiO2 | 20.23% | 95.8% |
Al2O3 | 5.79% | 0.18% |
Fe2O3 | 1.97% | 0.19% |
CaO | 62.02% | 0.30% |
K2O | NA | 0.29% |
Na2O | 0.77% (equiv.) | 0.20% |
MgO | 1.4% | 0.20% |
SO3 | 3.3% | 0.11% |
A reactive (siliceous) and a nonreactive (manufactured limestone) fine aggregate were used as a part of this study to produce two separate control UHSC mixtures. The siliceous sand contained quartz (64.0%), chert (17.1%), and feldspar (11.5%) and was procured from El Paso, TX. Previous research completed by Folliard et al. [
Mineral composition of foundry sand.
Compound | Foundry sand |
---|---|
MgO | 0 |
Al2O3 | 1.7 |
SiO2 | 94.1 |
K2O | 0 |
P2O5 | 0 |
CaO | 0.2 |
TiO2 | 0 |
MnO | 0 |
Fe2O3 | 5.8 |
Based on a literature survey, it is recommended to only use fine aggregate in UHSC mixtures in order to increase the particle packing density and therefore increase strength [
Grain size distribution for the sand.
Sieve number | Sieve size, mm (in.) | Percentage passing |
---|---|---|
Manufactured sand | ||
30 | 0.60 (0.0236) | 98.19 |
50 | 0.30 (0.0118) | 34.45 |
100 | 0.15 (.00591) | 3.14 |
|
||
Reactive sand | ||
30 | 0.60 (0.0236) | 98.39 |
50 | 0.30 (0.0118) | 20.4 |
100 | 0.15 (.00591) | 3.5 |
|
||
Foundry sand | ||
30 | 0.60 (0.0236) | 98.59 |
50 | 0.30 (0.0118) | 34.81 |
100 | 0.15 (.00591) | 4.24 |
Physical properties of aggregates and foundry sand.
Property | Standard | Unit | Manufactured sand | Siliceous sand | Foundry sand |
---|---|---|---|---|---|
Unit weight | ASTM C29 | kg/m3 (lb/ft3) | 1,432 (89.4) | 1,510 (94.3) | 1,411 (88.0) |
Water absorption | ASTM C127 | % | 1.94 | 0.99 | 0.08 |
Bulk specific |
ASTM C127 | — | 2.52 | 2.56 | 2.62 |
Bulk specific |
ASTM C127 | — | 2.43 | 2.52 | 2.62 |
The concrete mixtures were developed based on the literature [
Concrete mixture proportions.
Mixture |
Cement | Silica fume | Manufactured |
Reactive sand | Foundry sand | Steel fibers | HRWRA | Water |
---|---|---|---|---|---|---|---|---|
kg/m3 (lb/yd3) | kg/m3 (lb/yd3) | kg/m3 (lb/yd3) | kg/m3 (lb/yd3) | kg/m3 (lb/yd3) | kg/m3 (lb/yd3) | l/m3 (gal/yd3) | kg/m3 (lb/yd3) | |
NR-Cont | 890 (1500) | 222 (375) | 821 (1384) | — | — | 119 (200) | 29.7 (6) | 222 (375) |
NR-10FS | 890 (1500) | 222 (375) | 739 (1246) | — | 90 (152) | 119 (200) | 29.7 (6) | 222 (375) |
NR-20FS | 890 (1500) | 222 (375) | 657 (1108) | — | 180 (303) | 119 (200) | 29.7 (6) | 222 (375) |
NR-30FS | 890 (1500) | 222 (375) | 575 (455) | — | 270 (455) | 119 (200) | 29.7 (6) | 222 (375) |
RA-Cont | 890 (1500) | 222 (375) | — | 842 (1419) | — | 119 (200) | 29.7 (6) | 222 (375) |
RA-10FS | 890 (1500) | 222 (375) | — | 757 (1276) | 90 (152) | 119 (200) | 29.7 (6) | 222 (375) |
RA-20FS | 890 (1500) | 222 (375) | — | 673 (1134) | 180 (303) | 119 (200) | 29.7 (6) | 222 (375) |
RA-30FS | 890 (1500) | 222 (375) | — | 589 (992) | 270 (455) | 119 (200) | 29.7 (6) | 222 (375) |
NR: nonreactive (manufactured sand); RA: reactive aggregate (siliceous sand); FS: foundry sand.
The aggregates used in this study were sieved to obtain the desired size needed as described previously. The aggregates were then thoroughly washed over a number 200 sieve to remove any fine dust or debris. After washing, the aggregates were oven-dried at 44°C (110°F) for a minimum of 24 hours to achieve a 0% moisture content.
The constituents of each mixture were then mixed for approximately 20 minutes using a laboratory pan mixer. The dry constituents (aggregate, cement, and silica fume) were mixed for the first 2 minutes and then 75% of the water was added. After thorough mixing, the HRWRA was added with the remaining 25% of the water. This preparation method was used based on the literature and experience [
In order to minimize as many variables as possible, one curing regimen was tested for the compression testing samples, which was selected based on the literature review developed by Shaheen and Shrive [
Compressive strength specimens were molded using 50-mm (2-in.) cube molds. Cubes specimens were used to avoid problems with end preparation of cylindrical specimens [
Mortar samples from each mixture were used to monitor the heat development using a Calmetrix isothermal calorimeter suitable for paste, mortar, and concrete samples. A standard 23°C isothermal temperature was used in this experimental program. Immediately after mixing, roughly 50 grams was weighed and placed in plastic cup molds designed specifically for use in the calorimeter. The average hydration curves of two samples from each batch were used and are presented in the Results.
The accelerated mortar bar method (AMBT) ASTM C1567 [
A minimum of four prisms 25 × 25 × 285-mm [1 × 1 × 11.25-in] were used to determine the change in length as outline in ASTM C1567 [
The compressive strengths for the UHSC mixtures with different percentages of spent foundry sand at 7, 14, and 28-day curing are shown in Figures
Compressive strength of manufactured (nonreactive) sand: foundry sand mixtures at 7, 14, and 28 days.
Compressive strength of reactive sand: foundry sand mixtures at 7, 14, and 28 days.
The average control compressive strength for all ages was approximately 119 MPa (17,300 psi), which is well above the minimum compressive strength threshold set for UHSC mixtures. This result demonstrates that, at minimum, a UHSC mixture was produced and the impact of FS replacement is investigated. The mixtures incorporating FS ultimately demonstrate a loss in compressive strength with an increase in FS percentage. At 10% inclusion of FS, the average compression strength for all ages dropped to approximately 107 MPa (15,586 psi), which is approximately a 10% reduction in strength from the control. At a 20% fine aggregate replacement with FS, the average compressive strength for all ages dropped to approximately 102 MPa (14,849 psi), which is a 15% drop in compressive strength when compared to the control. Lastly, at a 30% FS replacement level, the compressive strength dropped to approximately 96 MPa (14,000 psi), which is 21% loss in compressive strength when compared to the control samples. To confirm if these results are statistically significant, Student’s
On the other hand, mixtures incorporating reactive siliceous sand showed substantially higher strength performance. The control mixture showed the highest compressive strength overall, exceeding 150 MPa (21,755 psi) after only 7 days of curing. Interestingly, a sharp reduction in compressive strength was noted after 14 days of curing for all mixtures with the exception of 20% foundry sand. This may be attributed to the self-desiccation of the low w/cm concrete mixture limiting the continued hydration for the additional formation of hydration product [
The control mixture reached a compressive strength of 181.78 MPa (26,365 psi), whereas mixtures RA-10FS, RA-20FS, and RA-30FS observed a compressive strength of 167.21 (24,252 psi), 137.70 (19,972 psi), and 137.90 MPa (18,550.33), respectively. This is contrary to what previous studies have shown that spent foundry sand used as a partial replacement of fine aggregate can improve the mechanical properties of concrete [
The potentials for alkali silica reactivity for both the nonreactive and reactive aggregates containing foundry sand are presented in Figures
Expansion curves of manufactured (nonreactive) sand: foundry sand mixtures.
Expansion curves of reactive sand: foundry sand mixtures.
Note that the prisms were cast using high capacity steel fibers as a part of the matrix. Thus, only minor changes in length were observed for both series of mixtures and well under the expansion limit of 0.10% for deleterious alkali silica reactivity as suggested by [
Cracking of reactive bars observed after 28 days in NaOH solution: (a) RA-30FS; (b) RA-10FS.
Isothermal calorimetry was chosen as the method for investigating the hydration of UHSC mixtures with various replacement of foundry waste. Isothermal calorimetry measures the heat flow from cement hydration reactions by differential heat flow sensors that allow for comparison of different mixtures and provide a time-lapsed understanding of the hydration mechanisms. The timing and shape of heat flow curves can provide an understanding of the performance of different cementitious systems. Additionally, heat flow curves combined with compressive strength data can provide insight on the mechanisms through which the addition of mineral admixtures such as foundry waste influences strength development.
The data from isothermal calorimetry test were used to plot curves showing the rate of heat produced during hydration and are presented in Figures
Heat of hydration summary for concrete mixtures.
Mix-ID | Avg. peak heat flow |
Deviation from control sample |
Avg. time until peak heat flow |
Deviation from control sample |
---|---|---|---|---|
NR-Cont | 2.04 | — | 13.58 | — |
NR-10FS | 2.06 | 0.02 | 12.30 | 1.28 |
NR-20FS | 2.15 | 0.11 | 10.92 | 2.67 |
NR-30FS | 1.98 | −0.06 | 10.77 | 2.82 |
RA-Cont | 1.64 | — | 12.65 | — |
RA-10FS | 1.66 | 0.03 | 12.90 | −0.25 |
RA-20FS | 1.71 | 0.07 | 12.63 | 0.02 |
RA-30FS | 1.55 | −0.09 | 12.40 | 0.25 |
Heat flow curves for UHSC-FS mixtures using nonreactive aggregate.
Heat flow curves for UHSC-FS mixtures using reactive aggregate.
From Figures
A sustainable, high strength concrete mixture using waste foundry sand was investigated in this study. Mechanical properties, hydration reactivity, and alkali silica reactivity were monitored on two series of UHSC mixtures blended with spent foundry sand up to 30% replacement of fine aggregate by volume. Based on the investigation, the following conclusions can be drawn: For both series of UHSC mixtures using nonreactive and reactive fine aggregate, a decrease in compressive strength was observed with the replacement of natural fine aggregate with that of foundry waste up to the 30% replacement investigated. UHSC mixtures using the reactive siliceous sand yielded the highest compressive strengths compared to those using the nonreactive manufactured sand. However, the minimum compressive strength observed was 85 MPa (12,345 psi) at the highest replacement level tested (30%) for the series of mixtures using nonreactive sand and is still considered UHSC. The alkali silica reactivity for mixtures containing foundry sand showed an increase in expansion with increasing replacement of foundry waste up to 30%. The effects are pronounced for those mixtures blended with foundry waste and reactive siliceous aggregate. The calorimetry data showed that the addition of foundry waste enhanced the growth of hydration products by providing extra nucleation and growth sites with their finer particle size distribution. This was very pronounced for the UHSC mixtures using nonreactive fine aggregate.
American Concrete Institute
American Society for Testing and Materials
Alkali silica reaction
Accelerated mortar bar test
Concrete Industry Management
Foundry sand
Granulated ground blast furnace slag
High range water reducing admixture
Nonreactive
Oven dry
Ordinary Portland cement
Reactive aggregate
Research Enhancement Program
Supplementary cementitious material
Saturated surface dry
Ultrahigh strength concrete
X-ray fluorescence.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors of this study would like to thank Research Enhancement Program (REP) at Texas State University for the support of this research. The authors would also like to thank Mr. Brady Gillar from Southwest Steel Casting Company for donating the foundry waste to their study. Lastly, thanks are due to the several undergraduate researchers in the Concrete Industry Management (CIM) program for their assistance in this work.