An Estonian gravel-road test developed cracks within months; 10 years later, a company says its stabilised soil gained strength

A gravel-road stabilisation test carried out in Estonia in 2015 is being presented by StabilRoad Holding as a decade-long example of increasing material strength. The company said in November 2025 that laboratory tests of core samples taken from the road every two years showed the compressive strength of the stabilised soil had increased by an average of 1.0 to 3.0 MPa over 10 years. However, the company’s online report does not provide baseline strength values, the number of samples or the testing procedure behind the 10-year comparison. Earlier research commissioned by Estonia’s Road Administration recorded transverse cracks in the same test area within weeks of stabilisation, as well as further defects during subsequent inspections.The 2015 test on road no. 24109The test was carried out in July 2015 on road no. 24109 Kõo–Kolga-Jaani, between kilometres 17.7 and 19.1, near Kolga-Jaani. A 2017 research report commissioned by the Estonian Road Administration said the road was divided into test sections of about 468 metres. One section used the InfraCrete soil-stabilisation material with cement, while another used M10+50 and LBS polymers with cement. The stabilised layer on the InfraCrete section was 30 cm thick. The report said a 1.5-times surface dressing was applied to half of the stabilised test sections in 2015, while the other half was initially left unsealed so that changes in the stabilised gravel layer could be monitored. The remaining part was repaired and surface-dressed in 2016.“The current StabilRoad project page describes the Kolga-Jaani project as having been carried out in July 2015. It says the road was later treated with bitumen emulsion and crushed stone in the second year, followed by a 4 cm asphalt layer in the fourth year.Earlier research recorded cracksThe 2017 Skepast&Puhkim report found that the InfraCrete section developed transverse cracks relatively soon after stabilisation. The report said the cracks appeared within about a month. By spring 2016, inspectors recorded 11 transverse cracks up to 5 mm wide, including three on the part that had already received surface dressing. The originally unsealed section also had areas of unevenness and small holes. By June 2017, the section remained drivable, but the originally unsealed portion was more uneven, and the test section still contained small holes and transverse cracks. The same report recorded the InfraCrete section’s elastic modulus at 569 MPa in 2015 and 596 MPa in 2016. Its comparison table also gave an average IRI roughness value of 3.06 mm/m for the section. The report also found that 5 tonnes of InfraCrete had been used, twice the planned quantity of 2.5 tonnes. It suggested that the difference may have resulted from a calculation error when the material was spread using a cement spreader.The Skepast&Puhkim report ultimately said the tested InfraCrete and cement stabilisation method was not suitable for constructing dust-free light pavements on low-volume roads when its operating costs and actual test results were taken into account. Its calculated 25-year discounted operating cost for the InfraCrete and cement treatment was €116,871 per kilometre, compared with €44,451 per kilometre for the surface-dressing alternative considered in the study.What the company says after 10 yearsStabilRoad Holding's November 2025 report presents a different picture of the section's longer-term condition. The company says it monitored the road for 10 years and took core samples every two years to assess changes in the compressive strength of the stabilised soil. According to the company, the strength increased by an average of 1.0 to 3.0 MPa over the decade. The company also says visual inspections found that the appearance of the stabilised road surface had remained unchanged from its original condition. Its project description says the section was surface-treated in the second year and received a 4 cm asphalt layer in the fourth year. StabilRoad further projects that the same level of stability and strength could persist for another 50 to 100 years.The 10-year result therefore comes from the company's own monitoring rather than the earlier Road Administration research programme. The online company report gives the reported increase of 1.0 to 3.0 MPa, but does not publish the baseline compressive-strength measurements, sample count or laboratory testing method needed to independently assess the magnitude of that increase. The earlier research, meanwhile, documents cracking during the first two years of the test. The two sets of records describe different stages of the same road experiment and measure different aspects of its performance.You use AI every day. Now get your AI Quotient. Take the AIQ test.