Long-term pavement performance experiments : a personal experience

The author shares his experience over the last 40 years of the design, monitoring and final evaluation resulting from 23 purpose-built road experiments consisting of over 200 individual sections plus many observation sections in Botswana, Namibia and South Africa. The purpose-built LTPP experiments and the lengths of existing road selected as observation sections are of four types. The first three are intended to show how to make the best use of local, low-cost materials for low to medium volume roads in the dry and moderate macroclimatic zones of southern Africa ? some two-thirds of the region: ? Bases and subbases of marginal to substandard (mostly G5-G7) calcrete, weathered granite, weathered basalt, neat (G7), cement- and bitumen-treated Kalahari sands, and sulphide- and acidic sulphate- contaminated gold and copper mine waste rock. ? Brack, saline and sea water for compaction of all layers including the base and in the slurry of a Cape seal. ? Selected calcrete as chippings in various types of seal coats in the Kalahari where conventional stone does not occur. The fourth type is intended to provide proven countermeasures to eliminate or at least mitigate the damage to roads on expansive clay roadbeds ? apart perhaps from drainage-related failures the most common form of roadbed-related distress in southern Africa. In all cases control sections of G3 crushed stone, G4 gravel, stabilized gravel, fresh water, or with no countermeasures as appropriate were included as part of the experiments. These experiments are proving ? by means of monitoring over periods in excess of 20 years ? that, for example, and depending upon traffic, substandard calcretes with PIs of 20, sulphidic and acid-saline mine rock, seawater and even unsound basalt can all be used successfully in the base course, and that the effects of expansive clays can be greatly reduced without incurring increased maintenance costs provided that certain precautions are taken. The design requirements and the problems of preserving and monitoring such long-term experiments are discussed. The advantages and disadvantages of LTPP vs HVS trafficking are discussed and it is concluded that a judicious mix of both is necessary.Paper presented at the 35th Annual Southern African Transport Conference 4-7 July 2016 "Transport ? a catalyst for socio-economic growth and development opportunities to improve quality of life", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US

The use of seawater in road construction: part 1 – the swartklip and lambert’s bay experiments

Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2023.Construction of a new road may require the daily use of upwards of 1 000 m3 of water – usually fresh – sufficient for 20 000 people at the Cape Town drought ration of 50 litres/day. The Swartklip experiment was therefore constructed in 1975 in a moderate macroclimatic area near Cape Town and the Lambert’s Bay experiment in a dry area of the Western Cape Province, South Africa, in order to ascertain how to use seawater for the compaction of graded crushed stone bases without incurring damage to the base during construction or compromising its long-term performance. After completion, the seawater crushed stone bases had salinities as determined by the saturated paste electrolytic conductivity test of 0,5 S/m in comparison with the freshwater controls of 0,06 and 0,08 S/m respectively, and the maximum of 0,15 S/m later normally permitted. After up to 30 years of monitoring both during and after construction, it is concluded that seawater can successfully be used in all layers of a flexible pavement with a graded crushed stone base under a 13 or 19 mm Cape seal for at least a 20-year design life, provided that certain precautions are taken in the design and during constructio

The biesiesvlei long-term plastic calcrete base experiment: performance over 30 years until failure

Calcretes are probably the most widely used road construction materials in southern Africa, rank second after dolerites in relative importance in South Africa and are often the only available materials in the vast area covered by Kalahari sands. After a back-analysis of some old calcrete-based roads in the Western and Eastern Cape in the 1960s indicated that substantial relaxations in plasticity, grading and even CBR might be possible, purpose-built LTPP experimental sections were constructed in Botswana, Namibia and South Africa in order to test this hypothesis. The performance of one of these – the Biesiesvlei plastic calcrete base experiment constructed in 1976 on the now N14-11 in the North West Province – until failure after 0,5 MESA in 30 years is described. Three simple specifications for a similar calcrete base for a Category C road in dry and borderline moderate macroclimatic regions for structural capacities of 0,3; 0,5 and 0,8 MESA were derived empirically from the comprehensive test and performance data collected. These all require a GM of 1,7 ‒ 2,5 and, depending on capacity, a maximum PI of 16 ‒ 14, a maximum LSM of 320 ‒ 260, and a minimum 98% soaked CBR of 40 ‒ 60.Papers presented at the 40th International Southern African Transport Conference on 04 -08 July 202

Gypsum in saline and non-saline road bases: effects and limits derived fr0m long-term road experiments in Namibia

In parts of Namibia, Botswana and South Africa the only economically available road construction materials often contain excessive amounts of highly soluble salts such as NaCl (common table salt) and/or gypsum (CaSO4•2H2O) and fresh water for compaction is scarce. The Lüderitz and Haalenberg full-scale, long-term road experiments were therefore constructed in 1976 in the Namib Desert in Namibia in order to find ways of successfully using highly saline and gypseous materials as road pavement base course and of using seawater for the compaction of all layers. In this paper only those aspects concerning gypsum are presented. The experiments included a total of eight sections of G3 quality crushed stone bases with 2 – 20% added gypsum and two of G4 calcrete base with 5% (in comparison with the then permitted limit of 3,5%), in addition to their natural gypsum contents of 0,2 and 0,3% respectively, all under a 19 mm Cape seal surfacing. These experiments were monitored both during and soon after construction as well as for any long-term effects over a period of 36 years from 1976 until 2012. During this period the experiment only received two rejuvenation sprays and a minor amount of slurrying, edge patching, crack sealing and shoulder regravelling. For a 30-year design life and a capacity of at least 1,0M E80 under a 19 mm Cape seal, gypsum contents of up to 10% can be permitted in a G3 and up to at least 5% in a calcrete G4 base in this arid environment and probably in most of the southern African arid and semiarid zone.Papers presented virtually at the 39th International Southern African Transport Conference on 05 -07 July 202

The use of seawater in road construction: part 2 – the lüderitz experiment

Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2025As freshwater is extremely scarce along the desert coast of Namibia ten experimental sections of graded crushed stone base compacted with either seawater or freshwater as controls were constructed in 1976 at Lüderitz. These sections included sections with seawater only up to subbase level and seawater in all layers, with and without 5% added gypsum in the base in order to simulate a gypseous binder, using freshwater base sections with and without 0,5% added NaCl as control sections, as well as certain compaction and construction time constraints. The mean salinity of the bases after compaction and slushing with sea or freshwater as measured by the paste electrolytic conductivity test were 0,4 – 0,5 S/m in the seawater sections in comparison with 0,15 S/m in the freshwater section with seawater only in the subbase and lower layers and 0,09 S/m in the section with freshwater in all layers, and the maximum of 0,15 S/m usually permitted No significant salt damage occurred to the primed base or to the surfacing during or after construction and after 35 years of monitoring it was concluded that at any time of the year under conditions similar to those at Lüderitz seawater can be used in all layers including a G3 base under a 19 mm Cape seal provided that certain precautions are taken

The use of seawater in road construction : part 3 – a quick guide to an accelerated construction method

Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2023.The usual South African requirement for the maximum soluble salt content of the base and subbase of a road to be covered with a bituminous surfacing as determined by the paste electrolytic conductivity (EC) test of 0,15 S/m is a conservative limit intended for normal use without requiring any special design or construction precautions. Compaction of most pavement materials with an inherently low EC of less than about 0,1 S/m with seawater or other comparable chloride-sulphate water with a salinity of about 3,5% will raise the EC to about 0,5 S/m, which exceeds even the maximum of 0,40 S/m usually specified for selected subgrade layers. A design and accelerated construction method was therefore developed from experience and research in order to enable the use of both inherently saline materials and waters with a salinity up to about that of seawater for compaction with little risk of salt damage. This essentially involves covering each layer with the next as soon as practicable in order to minimise upward migration during construction and then priming and sealing the base as soon as practicable with an impermeable surfacing in order to keep the salt safely in solution. The maximum target delays between the pavement layers derived from local experience and LTPP experiments together with additional precautions are summarised, together with comments on evaluating water for road compaction

Experimental rehabilitation of a road with intractable salt damage with a bitumen-rubber single seal

Bituminous surfacings which have been blistered, cracked and potholed due to excess salt in the base course are notoriously difficult to rehabilitate by resurfacing with a seal or asphalt as the damage usually penetrates the new surfacing within one year. This paper describes an experiment laid in 1984 on the O’kiep-Steinkopf road (now the N7/8) in Namaqualand to rehabilitate with 7 mm bitumen-rubber single seals at application rates of 2,6 - 3,6 l/m2 . A length of 728 m of an extensively salt-damaged 19 mm Cape seal with two reseals which was still developing new salt damage more than 20 years after construction in 1961, and a very lightly trafficked dead-end remnant cut off from the 1961 road and resealed once was used. On both sections the damage on the existing surfacing consisted of patches of mostly 50 mm diameter craters and blisters averaging about 75 mm in diameter at a spacing of 0,5 - 2 m on the road (some 4 000 / km), and 300 mm on the remnant, together with 1 - 3 mm-wide cracking on a starburst to random pattern, closed blisters, and staining. Although within one year all the experimental reseals on both sections were also penetrated by salt damage, after five and eight years the bitumenrubber seals on the lightly trafficked section (intended to simulate the worst-case scenario of surfaced shoulders and airports) were in a fair condition and remained so for 13 years whereas the unresealed control sections were severely and extensively potholed. After two years the unmaintained 12 half-width bitumen-rubber sections exhibited an average of 11 blisters (closed and cratered) / 100 m and 55 blisters plus stains (potential blisters) / 100 m in contrast to 47 blisters and 83 stains on the emulsion control section and 9 blisters, 5 stains and 178 patches (some prior to 1984) on the two untreated 1980 control sections. After five years before a routine reseal of the whole road in 1989 the bitumenrubber exhibited negligible damage and no patching, whereas both were present on the emulsion and 1980 seal controls. Although after eight years in 1992 even the 1989 (the fourth) reseal had become slightly damaged, in 1997 after a further reseal no damage was visible except for a few stains on the emulsion-sealed section, and none at all after 20 years. It is concluded that an ordinary single reseal should not be used on a salt-damaged seal, that a bitumen-rubber single reseal at a minimum of 2,8 l/m2 should be an acceptable although not a perfect solution, and that the sulphide as well as the salt content and pH should also probably be controlled in base coursesPapers presented at the 40th International Southern African Transport Conference on 04 -08 July 202

The Jwaneng LTPP Experiment: Performance Over 14 Years and a Comparison Between Kalahari Sand- Asphalt and Calcrete Base Courses

The Jwaneng long-term pavement performance base course experiment on the Kanye-Jwaneng road in Botswana consisted of 12 test sections of wet-mix and foamed Kalahari sand-asphalt and 11 test sections of mostly substandard calcrete base course with two control sections of gravel base, all under a double surface treatment. The purpose of the experiment was to evaluate various alternative base material quality designs for roads in the Kalahari where good quality gravels are scarce. Although the performance of most of the sand-asphalts and some of the calcretes was marred by construction defects, monitoring for 13 years and 0,4 ME80 showed that both types of base course were viable options for at least 1,0 ME80 and that untreated calcretes previously regarded as too inferior could be used as base course. The performance of the cement, lime and mechanically stabilized calcretes was inferior to that of their untreated equivalents.Papers presented at the 38th International Southern African Transport Conference on "Disruptive transport technologies - is South and Southern Africa ready?" held at CSIR International Convention Centre, Pretoria, South Africa on 8th to 11th July 2019

The orapa emulsion-treated kalahari sand experiment: performance over 30 years and derived material and pavement designs

The purpose of this experiment on the Serowe-Orapa road in Botswana constructed in 1989 was to evaluate the performance of both grey and red fine Kalahari sands treated with SS60 emulsion both in the upper half only and the full 150 mm of the base. After 19 years of regular performance monitoring and 0,3 MESA, ten test and three control sections were still in a good to very good condition and all were still in a satisfactory condition after 30 years and a projected 0,5 MESA. The red sand sections performed better than the grey and only the 2,5% emulsion half-depth grey sand section failed. Maintenance applied over the first 20 years was a fog spray, two reseals and patching of edge breaks, mole tunnel depressions and, on two grey sand sections, base course shear failures. CBR and UCS empirical laboratory design guidelines for SS60 ETBs for both grey and red sands with 2,5 – 6,5% emulsion as well as the requirements for the raw sand and the whole pavement, are presented. The most economical designs are red sands with 2,5% emulsion in the upper base only for up to a projected 0,8 MESA and 2,5% in the whole base for up to 1,0 MESA for a Botswana Category II or a South African Category C road.Papers presented virtually at the 39th International Southern African Transport Conference on 05 -07 July 202

Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability