This paper presents findings from a preliminary study to assess the structural and material properties of a nonstandard, concrete type mix containing RoadCem, a traditional soil stabilising additive. Two different mixes determined the effect of adding RoadCem in terms of compressive and flexural strengths, breaking strain, thermal expansion and contraction behaviour, permeability using a falling head, and Young’s modulus. RoadCem is a fine powder containing alkali metals and synthetic zeolites which are complemented with a complex activator. RoadCem modifies the dynamics and chemistry of cement hydration by enhancing the crystallisation process and forming longer needle crystalline structures. It reduces the heat of hydration with an early strength development. Varying the volume in the mix varies the viscosity and alters curing times while maintaining the water cement ratio. The results from this study have shown a modest increase in compressive strength and Young’s modulus with improvements in thermal performance, particularly at low temperatures. The flexural strength of the two mixes was similar with a much reduced permeability in the RoadCem mix. The results demonstrate the improved performance of concrete incorporating RoadCem but further improvements are possible by using a better graded aggregate and controlling the maximum dry density and moisture contents.
RoadCem is a fine powered cement-based soil stabiliser used on earthworks, motorway, and hydraulic engineering projects [
By combining with the soil, the addition of RoadCem changes the mineralogical structure leading to a strong, durable crystalline structure which is fibrous in nature [
Previous work into the addition of cement-based soil stabilisers in concrete investigated the effect of variables including compaction friction, specimen size, compaction delay, and curing conditions encountered in laboratory environments [
Little research has been undertaken to assess the improvements RoadCem can make to the structural properties of concrete. Its addition reduces the heat production during hydration and limits the need for additional additives [
In order to assess the effect of RoadCem in concrete and its potential as a RCC or THL, an experimental investigation was carried out at the Dublin Institute of Technology, Ireland. As RoadCem is known to produce a zero-slump material, it was decided to study the effect of the additive on the structural (compressive strength, flexural strengths, and Young’s modulus), thermal (freezing and thawing), and durable (permeability) performance of different mixes. The samples included a plain CEM I mix and another containing RoadCem. The results of this study are reported and discussed in this paper and the findings show the potential of the additive to improve the structural properties and thermal performance while offering suggestions to improve the permeability.
Two mixes were cast for this study, plain incorporating only CEM I cement and a second with the RoadCem additive with 1% by weight of cement both with a fixed w/c ratio of 0.60. The cement content of the plain and the RoadCem concretes was 19.4 and 76.7 kg/m3, respectively. The cement volume increased in the second mix to account for the minimum PowerCem requirement of 50 g [
A summary of the mixes cast and details are shown in Table
Mix proportions.
Mix ID | Mass of ingredients (kg/m3) | ||||
---|---|---|---|---|---|
CEM I | Water | FA | CA | RoadCem | |
1 | 19.4 | 11.7 | 56.3 | 227 | 0 |
2 | 76.7 | 46 | 222.1 | 894.7 | 0.767 |
FA: fine aggregate, CA: course aggregate.
CEM I (Strength Class 42.5 N) cement complying with EN 197-1, Cement: Composition, Specifications and Conformity Criteria for Common Cements [
The mixes were manufactured using a pan mixer with six 150 × 150 × 150 mm3 cubes, three 100 × 100 × 500 mm long beams, six 75 × 75 × 285 mm long prisms, and four 100 mm diameter × 130 mm long cylinders cast.
After mixing, the materials were poured in 50 mm thick layers, into the moulds with each layer vibrated on a vibrating table for a time. However, it was observed that this did not adequately compact the concrete so a jack hammer compactor rammer was used with a 100 × 100 mm2 tamping plate connection. Curing was provided by placing a polythene sheet over the specimens for 24 hours to trap moisture that evaporates from the surface. Following demoulding, the samples were placed in water in a curing tank at 20 (±1)°C until testing.
The compressive strength was determined by crushing three 150 mm cubes at 7 and 28 days for each mix in accordance with EN 12390-3 for testing hardened concrete [
The flexural strength was determined by breaking three 100 × 100 × 500 mm long beams at 28 days for each mix in accordance with BS 1881 Testing hardened concrete [
Flexural beam tests (a) during test and (b) with a strain gauge attached.
Young’s modulus was determined using the 150 mm cubes at 28 days. The cubes were chosen as a better bond between the strain gauges (5 mm long Tokyo Sokki Kenkyujo strain gauge type YFLA with a gauge factor of 2.10 ± 2%) and the concrete is possible. The cubes were loaded up to 1/3 of the failure strength, repeated three times with the slope of the stress-strain graph under load in the third cycle used for calculating Young’s modulus. The concrete setup prior to testing is shown in Figure
Cube with strain gauge attached to determine Young’s modulus.
The thermal analysis was carried out on the 75 × 75 × 285 mm prisms by placing in a heater and freezer at 80°C and −15°C, respectively, for 24 hours at 28 days old. The change in length was determined using the apparatus shown in Figure
Sample prisms undergoing thermal (a) expansion and (b) contraction.
The coefficient of permeability of the samples was determined using the falling head apparatus shown in Figure
Samples undergoing the falling head permeability test.
The compressive strength results at 7 and 28 days are presented in Figure
Compressive strength results.
Firstly, the cement content was low. This is a feature of RCC which prioritises flexural above compressive strength. While the amount of cement in the RoadCem is higher, the w/c ratio of 0.6 was maintained and the other constituents of the mix were also maintained. Secondly, the aggregate used was low grade with insufficient fines (passing a 63
The flexural strength of the two mixes at 28 days is shown in Figure
Flexural strength results.
Flexural strengths of concrete are typically 10% of the compressive. From Figure
The flexural strain results are shown in Figures
Flexural strain readings.
The results show the rate of strain increase during loading for the RoadCem (Figures
The results indicate that the plain mix is more flexible with yielding occurring before ultimate failure where the RoadCem samples sustain the load until breaking [
Young’s modulus of the plain and RoadCem concrete is shown in Figure
Comparison of
Plain mix | PowerCem mix | ||
---|---|---|---|
Measured |
Calculated |
Measured |
Calculated |
4.7 | 4.8 | 5.3 | 5.7 |
Young’s modulus results.
The results of the thermal analysis are shown in Tables
Changes in length due to heating.
Plain concrete | RoadCem concrete | ||
---|---|---|---|
Oven at 80°C for 24 hrs | Oven at 80°C for 24 hrs | ||
Sample number |
|
Sample number |
|
1 | +0.002 | 1 | +0.11 |
2 | +0.137 | 2 | +0.101 |
3 | 0 | 3 | +0.002 |
Changes in length due to cooling.
Plain concrete | RoadCem concrete | ||
---|---|---|---|
Oven at −15°C for 24 hrs | Oven at −15°C for 24 hrs | ||
Sample number |
|
Sample number |
|
1 | −1.653 | 1 | −0.005 |
2 | +0.029 | 2 | −0.001 |
3 | −0.249 | 3 | −0.003 |
Figure
Flexural strength results following thermal analysis.
The permeability results are shown in Figure
Coefficient of permeability results.
On the basis of the various investigations carried out to assess the performance of cementitious materials containing the RoadCem additive, the following conclusions have been drawn.
(1) The compressive strength was shown to increase with the addition of RoadCem compared with the plain mix. The flexural strengths and rates of strain increase are similar in both. There is a slight increase in Young’s modulus in the RoadCem sample which is consistent with the flexural strengths and increase in strain rates during loading.
(2) The permeability of the RoadCem mix was noticeably less than the plain sample due to the uneven distribution of aggregates which created an open pore structure.
(3) The thermal performance of the RoadCem mix is much improved, particularly at low temperatures compared with the plain mix. The flexural strength of RoadCem following heating and cooling is also improved.
(4) Improvements in the results would be expected if a better graded aggregate was used corresponding with a Fuller-Thompson grading curve with sufficient fines passing a 63
(5) As shown above, drying the aggregates and using a Proctor analysis to control the maximum dry density and moisture content would also yield improvements.
The author declares that there is no conflict of interests regarding the publication of this paper.
The author wishes to acknowledge the funding provided by Invest NI Innovation Voucher programme which provided the financial support for this work. The author also thanks the technical support and the facilities of the School of Civil & Structural Engineering in DIT Bolton Street and gratefully acknowledges Turley Brothers Ltd.