Pavement and Materials Design Manual 1999 - CHAPTER 7

(1)

Cha

pter

7

Pavement and Materials Design Manual - 1999

Pavement

Materials

Project appraisal

Environment Pavement Design-New Roads Cross Section,

Shoulders and Drainage Traffic Subgrade Problem Soils

DESIGN ELEMENTS

Pavement Rehabilitation Bituminous Surfacings Gravel Roads

STR

UCTURAL

DESIGN

Comparison of alternatives and selection of design

Refinement of design, if required

Ch Ch

Pavement Materials

(2)

Chapter 7 Pavement Materials

Comments:

7.0 General

This chapter defines the physical properties for materials to be used in the pavement structure and forms an essential part of the method for design of new roads as given by the design catalogue, and rehabilitation design for existing roads. Requirements for materials in bituminous surfacings and gravel roads are given in /Chapter 10/ and /Chapter 11/ respectively. Within the limitations given in this chapter, materials used in the structural layers of the pavement shall be selected according to criteria of availability, economic factors and previous experience.

All materials are indicated by means of codes, e.g. G80, C2, CM, etc., which refer to materials with certain defined properties prescribed in this chapter. For the sake of consistency and ease of reference, the same codes are used in the pavement design catalogue and elsewhere in the manual where reference is being made to material types with specific properties. As far as possible all material types commonly used in the country are included, e.g. natural gravel/soils, processed or crushed materials, materi-als stabilised with cement or lime and bituminous materimateri-als.

.

7.1 Material Types

7.1.1 Crushed, fresh rock or boulders

Materials made by crushing and screening of hard rock sources of a variety of rock types can be used in layer work and in bituminous materials provided they meet the respective material standards. Two different qualities are used for layer work, CRR or CRS, depending on the type of source and the refinement of the quarry product. Crushed materials of qualities falling below the material classes CRR and CRS shall be denoted G80 or lower as appropriate.

7.1.2 Weathered rocks and laterites

General

Weathered rocks and laterites are common sources for pavement materials in the category of natural gravel and as a source for production of chemically stabilised materials. Laterites are highly weathered materials formed in a secondary process where the hydrated oxides of iron or aluminium have been accumulated in sufficient concentrations to affect the physical character of the deposits where they occur /7 - 8/.

Basic igneous rocks

Weathered rocks of basic igneous origin, such as basalt and dolerite, may release additional plastic fines during construction and in service, and thereby cause loss of strength over time. Such materials may require specialised additional laboratory testing to verify their long term durability. Tests of durability /7 - 3/ may include.

n chemical tests such as Sodium or Magnesium Sulphate Soundness tests (SSS or MSS)

Details on the method to assess data from the quality control of material properties are given in Standard Specifications for Highway Construction.

References to the relevant standards are given in Standard Specifications for Highway Construction for manufactured materials such as lime, cement and bitumen.

One test method alone is often insufficient to describe the durability of the rock and observations of past performance is in-valuable supplementary information where the deposit has been used previously. It is important to consider quality variations within one rock deposit where performance data are used in the assessment of durability.

(3)

Chapter 7 Pavement Materials

Comments:

n investigations of mineralogy by counts of secondary minerals

n physical tests by aggregate crushing in wet vs. dry condition or modified ball mill tests with studies of associated changes in grading and Atterberg limits after testing

Reference is made to the Central Materials Laboratory of Ministry of Works for appropriate procedures to test durability.

7.1.3 Coral rock and calcrete

General

Coral rock is a major source for pavement materials along the coast, where alternative sources of hard rock or good gravel are generally unavailable within short distances. Calcretes are formed under favourable conditions in dry and moderate climatic zones in a secondary process where calcium carbonate have been accumulated in sufficient concentrations to partly or fully alter or replace the host material thereby affecting the physical character of the deposits where they occur. Both calcretes and coral rocks typically have large variations in quality within a deposit and require careful selection and stockpiling.

Laboratory tests

The Atterberg limits of coral rocks and calcretes will appear artificially high as a result of the typical low specific gravity and the high water absorption of the particles often seen in these materials. Standard grading tests may give a distorted impression of the particle distribution in the material due to varying specific gravity of particles having different size within one sample. The design limits of coral rocks and calcretes are therefore modified compared to the general requirements and grading envelopes are not given for these types of materials.

.

7.1.4 Volcanic tuff (scoria)

Volcanic tuff often fail to meet pavement material standards due to low particle strength and can give construction problems even when meeting required material standards for layer work. This is due to poor

compactability caused by their open grain structure and a rough particle shape. Admixture of suitable fines can greatly improve workability, reduce the breaking of particles during construction and give acceptable results.

7.1.5 Self-cementing materials

Certain types of natural gravel such as some pedogenic materials - e.g. calcrete and laterite - are known to exhibit self-cementing properties in pavement layers, possibly caused by suction. Such materials would require specialised testing and evaluation before any favourable self-cementing properties can be taken advantage of in the pavement design.

Drying of material during testing of Atterberg limits is carried out at 60o_{C for}

calcrete and coral rock, in accordance with guidelines of Central Materials Laboratory of Ministry of Works.

The use of special compaction equipment such as grid rollers can be beneficial under circumstances where breaking of particles is desirable.

Petrifaction test of the soil fines and tests of CBR after wet/dry cycles or others may be used to identify self-cementing properties in soils /7 - 3/ and /7 - 4/.

(4)

Chapter 7 Pavement Materials

Comments:

7.2 Unbound Materials

7.2.1 Natural gravel

Classification

The natural gravel category includes granular materials - without any admixture of stabilisers - having the following composition:

n 100% natural gravel, or

n natural gravel with such small proportions of crushed particles that the material properties are almost identical to the uncrushed portion Pavement materials falling into this category are shown in Table 7.1.

Table 7.1 Natural gravel, material classes

Material requirments

Natural granular pavement materials shall comply with the requirements in Tables 7.2 and 7.3.

Table 7.2 Material requirements - G80 and G60

Material CML test

properties method

Wet or moderate climatic zones: min 80 after 4 days soak Wet or moderate climatic zones: min 60 after 4 days soak CBR [%] Dry climatic zones (both requirements shall be met): Dry climatic zones (both requirements shall be met):

at 98% MDD of min 80 at OMC of BS-Heavy min 60 at OMC of BS-Heavy 1.7 and BS-Heavy min 60 after 4 days soaking min 45 after 4 days soaking 1.11

General Coral rock, calcrete or General Coral rock, calcrete or

Atterberg requirements other calcified materials requirements other calcified materials

limits 1) Wet or Dry Wet Dry or Wet Dry or Wet Dry or moderate climate climate moderate climate moderate climate moderate

max LL [%] 30 40 35 45 35 45 40 45 1.2 max PI [%] 8 14 10 16 10 16 12 18 1.3 max LS [%] 4 7 5 8 5 8 6 9 1.4 Grading, sieve sizes [mm] 63 37.5 Grading requirements:

20 -dMAX shall be maximum 2/3 of the compacted layer thickness

5 -Grading Modulus (GM *) ): min 2.0

2 *)

0.425 GM = [ 300 - (% passing 2mm) - (% passing 0.425mm) - (% passing 0.075mm) ] / 100

0.075

Particle TFVdry: min 80 kN TFVdry: min 50 kN

strength TFVsoaked : min 60% of TFVdry TFVsoaked : min 60% of TFVdry

Soluble salts Where the gravel is used under a surface treatment, soluble salt content is assessed in accordance with /7-11/.

Field density

CBR - swell [%] max 0.5 max 1.0

measured at BS-Heavy compaction measured at BS-Heavy compaction

30 - 65

1) It is emphasised that the Atterberg limits shall be measured according to CML test methods 1.2, 1.3 and 1.4. These methods follow BS procuders and Nominal value: min 98% of MDD, BS-Heavy

utilise BS equipment. Other laboratory test procedures are likely to give results that are not comparable with the given material requirements. 1.7 2.7 10 - 30 20 - 50 Material class 5 - 15 100 80 - 100 60 - 95 Grading envelope, G80 [% passing] G80 G60

(no envelope for G60, coral rock, calcrete or other calcified materials) s s a l c l a i r e t a Materialclass Materialclass Materialclass MMaterialclass CCCCChhhhhaaaaarrrrraaaaacccccttttteeeeerrrrriiiiisssssitititititcccccsssss 0 8 G -- CtheBcRlasmsiinnc.lu8d0e%scrushedmateiralswhere lessthan50%by e c a f d e h s u r c a s a h e v e i s m m 5 e h t n o d e n i a t e r s e l c it r a p f o s s a m 0 6 G CBRmin.60% 5 4 G CBRmin.45% 5 2 G CBRmin25%

(5)

Chapter 7 Pavement Materials

Comments: Table 7.3 Material requirements - G45 and G25

7.2.2 Crushed materials

Classification

The category includes crushed granular materials - without any admixture of stabilisers - where the full range of particle sizes from fines up to the max. nominal size are included. The pavement design catalogue uses two basic qualities of crushed base course materials, as described in Table 7.4. The classes of pavement materials falling into this category are shown in

Table 7.4.

Table 7.4 Crushed materials, material classes

Material requirements

Crushed granular materials for pavement layers shall comply with the requirements in Table 7.5.

Material CML test

properties method

Wet or moderate climatic zones: min 45 after 4 days soak Wet or moderate climatic zones: min 25 after 4 days soak CBR [%] Dry climatic zones (both requirements shall be met): Dry climatic zones (both requirements shall be met):

at 95% MDD of min 45 at OMC of BS-Heavy min 25 at OMC of BS-Heavy 1.7 and

BS-Heavy min 25 after 4 days soaking min 15 after 4 days soaking _1.11

General Coral rock, calcrete or General Coral rock, calcrete or

Atterberg requirements other calcified materials requirements other calcified materials limits 1) Wet or Dry Wet Dry or Wet or Dry Wet Dry or

moderate climate climate moderate moderate climate climate moderate

max LL [%] 40 45 45 50 45 50 45 55 1.2 max PI [%] 14 18 16 20 16 20 18 24 1.3 max LS [%] 7 9 8 10 8 10 9 12 1.4

Grading *)

Modulus (GM) *)

GM = [ 300 - (% passing 2mm) - (% passing 0.425mm) - (% passing 0.075mm) ] / 100

Particle size dMAX shall be maximum 2/3 of the compacted layer thickness

Soluble salts Where the gravel is used under a surface treatment, soluble salt content is assessed in accordance with /7-11/.

Field density

BS equipment. Other laboratory test procedures are likely to give results that are not comparable with the given material requirements.

Nominal value: min 95% of MDD, BS-Heavy

G45

G25

_{1) It is emphasised that Atterberg limits shall be measured according to CML test methods 1.2, 1.3 and 1.4. These methods follow BS procuders and utilise} 1.7 Material class

min 1.5 min 1.2

CBR - swell [%] max 0.5 max 1.0

measured at BS-Heavy compaction measured at BS-Heavy compaction

s s a l c l a i r e t a Materialclass Materialclass Materialclass Materialclass M CCCCChhhhhaaaaarrrrraaaaacccccttttteeeeerrrrriiiiisssssitititititcccccsssss R R C , s r e d l u o b d e h s u r c , e g r a l r o k c o r d e h s u r c , h s e rf -r e t e m a i d m 3 . 0 > e v it c ir t s e r e r a s t n e m e ri u q e r -e v it c ir t s e r e r a s t n e m e ri u q e r n o it c a p m o c -S R C l e v a r g m o rf e z i s r e v o d e h s u r c s e d u l c n i s s a l c e h t -d n a s r e d l u o b f o s e c r u o s n i-ll a d e h s u r c , s e c r u o s s e it il a u q d e t c e l e s f o s k c o r l a r o c d e h s u r c e h t n o d e n i a t e r s e l c it r a p f o s s a m y b % 0 5 . n i m -e c a f d e h s u r c e n o t s a e l t a e v a h ll a h s e v e i s m m 5

It should be noted that the requirements for compaction of CRR materials are very high and are normally not achieved unless special techniques such as slushing with water are applied during construction. This type of material is therefore never prescribed unless a subbase stabilised with cement or lime is used in order to provide a firm platform for construction of the base course enabling slushing to be safely carried out without softening of the subbase.

(6)

Chapter 7 Pavement Materials

Comments: Table 7.5 Material requirements - CRR and CRS

7.3 Cemented materials

7.3.1 Classification

Cemented materials described in this manual include all natural or crushed materials where a stabiliser of cement or lime has been admixed. The classes of cemented materials are shown in Table 7.6.

Table 7.6 Cemented materials, material classes

7.3.2 Material requirements

Cemented materials shall comply with the requirements in Table 7.7.

Material CML test properties method Material source max LL [%] 1) 1.2 max LS [%] 1) 1.4 Grading, sieve

sizes [mm] Coarse Type Fine Type Coarse Type Fine Type

50 100 37.5 100 90 - 100 100 28 87 - 97 100 75 - 95 90 - 100 20 75 - 90 87 - 97 60 - 90 65 - 95 10 52 - 68 62 - 77 40 - 75 40 - 70 5 38 - 55 44 - 62 29 - 60 29 - 52 2 23 - 40 27 - 45 20 - 45 20 - 40 1,18 18 - 33 22 - 38 17 - 40 15 - 33 0,425 11 - 24 13 - 27 12 - 31 10 - 24 0,075 4 - 12 5 - 12 5 - 15 4 - 12 Aggregate strength

Soluble salt content For aggregate used under a surface treatment, soluble salt content is assessed in accordance with /7-11/.

Field density requirements

4

of MDD BS-Heavy Nominal value: min 100%

Material class CRR [% passing] [% passing] CRS 3 35

Nominal value: min 88% 30

1) It is emphasised that Atterberg limits shall be measured according to CML test methods 1.2, 1.3 and 1.4. These methods follow BS procuders and utilise BS equipment. Other laboratory test procedures are likely to give results that are not comparable with the given material requirements.

2.7 1.7

TFVdry: min 110 kN

TFVsoaked: min 75% of TFVdry TFVsoaked : min 60% of TFVdry

of Aggregate Density

Crushed rock. Shall be made by crushing and screening of fresh quarried rock or clean, un-weathered boulders of minimum 0.3 m diameter. All particles shall be crushed, no soil fines allowed.

Crushed stone. Made by crushing and screening of blasted rock, stones, boulders and oversize from natural gravel. Min 50% by mass of particles larger than 5 mm shall have at least one crushed face. Max 30% of material passing 5 mm can be soil fines.

s s a l c l a i r e t a Materialclass Materialclass Materialclass MMaterialclass CCCCChhhhhaaaaarrrrraaaaacccccttttteeeeerrrrriiiiisssssitititititcccccsssss 4 C e t e r c n o c n i e s a b b u s s a d e s u -a P M 4 . n i m S C U -s t n e m e v a p s a y ll a n i m o n y ti l a u q f o s l a ir e t a m e c r u o s m o rf e d a m -s t n e m e ri u q e r d e if i d o m h ti w -S R C 2 C a P M 2 . n i m S C U -s a y ll a n i m o n y ti l a u q f o s l a ir e t a m e c r u o s m o rf e d a m -s t n e m e ri u q e r d e if i d o m h ti w -5 4 G 1 C --mUCadSemrfionm.1sMouPracemateiralsofqualtiynominallyas s t n e m e ri u q e r d e if i d o m h ti w -5 2 G M C --mUCadSemrfionm.0s.5ouMrcPeamamteoirdailsifeodfmquaateltiyiranlominallyas s t n e m e ri u q e r d e if i d o m h ti w -7 G Material class C4 will normally be used as

subbase in concrete pavements and material standards are not given here. Comments:

(7)

Chapter 7 Pavement Materials

Comments: Table 7.7 Material requirements - C2, C1 and CM.

7.3.3 Type of stabiliser

The stabiliser shall be Ordinary Portland Cement or lime meeting the requirements of BS-890. Hydrated lime or quicklime may be used, but a programme describing the safety precaution for protection of personnel shall be established on sites where quicklime is used.

Table 7.8 gives the best suited type of stabiliser to use depending on the

soil properties.

Table 7.8 Selection of stabiliser for cemented materials

7.3.4 Content of stabiliser

The design content of stabiliser, expressed as a percentage of the dry weight of the soil, is determined according to CML tests 1.19, 1.20,1.21 and 1.22 and shall not be less than the minimum content found in the test of Initial Consumption of Lime (ICL). Where mixing on the road is employed the content used in the field shall exceed the design content from laboratory tests by 1% - point.

Material _{CML test}

properties C2 C1 CM method

Earthworks quality soils/gravel

min UCS [MPa] 2,0 1,0 0,5 1.21

ICL - test 1.22

max PI after stabilisation [%] 1) 8 8 8 1.2 and 1.3

Before stabilisation:

min CBRsoaked [%]

at 95% MDD of BS-Heavy

max PI [%] 1) 20 25 35 1.2 and 1.3

min 1.5 min 1.2

Particle size, dMAX

Aggregate strength TFVdry: min 50 kN - - 2.7

Field density Nominal value: min 97% of MDD BS-Heavy

Grading modulus *)

Nominal quality of source material - with requirements as given here

1.11

1.7

The content of organic matter should not exceed 0.5% - 1% - 2% for C2 - C1 - CM materials respectively. Source material

Material class

dMAX to be max 2/3 of compacted layer thickness

Stabiliser content [ %design ] shall be minimum the initial consumption of lime (ICL) value

*)

GM = [ 300 - (% passing 2mm) - (% passing 0.425mm) - (% passing 0.075mm) ] / 100

30 20

-Subbase quality soils/gravel

High contents of organic matter will increase the demand for stabiliser to achieve the required Unconfined Com-pression Strength (UCS) for the material.

The ICL is the amount of stabiliser consumed in the initial ion exchange reaction and is a required minimum content when using cement or lime. Below this amount of stabiliser one will not achieve a permanent gain in strength. e h t g n i s s a p % passingthe % passingthe % passingthe % passingthe % 5 7 mmmmmmmmmmsssssiiiiieeeeevvvvveeeee PIPIPI[PPI%I ] BBBBBsteeeeeasssssbtttttisssssilsuuuuuetititititireeeeeddddd % 5 2 n a h t s s e L r o % 6 n a h t s s e l s i I P 5 7 . s s a p % ( x I P mm) 0 6 n a h t s s e l s i cementonly ) 1 0 1 -6 cementpreferred 0 1 n a h t e r o m cementor ilme % 5 2 n a h t e r o M 0 1 n a h t s s e l cementpreferred 0 2 -0 1 cementor ilme 0 2 n a h t e r o m ilmepreferred 2) ) 1 _L_i_m_e_r_e_q_u_ri_e_s_p_r_e_s_e_n_c_e_o_f_c_l_a_y_p_a_r_it_c_l_e_s_t_o_r_e_a_c_t_a_n_d_i_s_t_h_e_r_e_f_o_r_e_u_s_e_d_f_o_r_m_a_t_e_ir_a_l_s r e w o p d e ri f l a o c m o rf h s a l e u f d e s ir e v l u p s a h c u s , s n a l o z z o p f o e r u t x i m d A .I P h g i h h ti w .I P w o l h ti w s l a ir e t a m r o f o s l a e l b i s s o p e m il h ti w n o it a s il i b a t s e k a m n a c , s t n a l p ) 2 _C_e_m_e_n_t_i_s_t_h_e_p_r_e_f_e_rr_e_d_s_t_a_b_i_il_s_e_r_f_o_r_m_a_t_e_ir_a_l_s_w_ti_h_l_o_w_P_.I_H_o_w_e_v_e_,r_c_e_m_e_n_t_c_a_n_b_e s i l a ir e t a m e h t f o y ti li b a k r o w e h t d e d i v o r p I P h g i h h ti w s l a ir e t a m f o n o it a s il i b a t s r o f d e s u . n o it a s il i b a t s t n e m e c o t r o ir p e m il % 2 h ti w t n e m t a e rt -e r p y b d e v o r p m i

Large amounts of stabiliser causes excessive crack developments in the cemented layer.

Lime can be successfully used for stabilisation of some calcified materials even when the PI is low.

TRL-Road Note 31 /7 - 7/ and South Africa TRH 13 /7 - 9/ refers for guidelines on the use of pozzolans and for further details about the stabilisation process in general. Comments:

(8)

Chapter 7 Pavement Materials

Comments: If a stabiliser content in excess of 4-5% is required then consideration

shall be given to selecting better qualities of materials to stabilise.

7.3.5 Construction

Time limits

Table 7.9 gives the maximum allowed time from the stabiliser has come

in contact with the material until compaction and finishing of the layer is completed.

Table 7.9 Cemented materials, time for completion of the layer

Curing - general

The cemented layer shall be kept moist and sealed off as soon as possible after completed compaction. Curing is essential for proper gain in strength by preventing drying out of the layer. Curing is also important to prevent future loss of strength in the cemented material by carbonisation caused by exposure to air. Curing by continuous watering shall be restricted to the period from completed construction until the curing methods described below are in place according to the time limits given.

Curing method - cemented base course

A bituminous curing membrane shall be applied without undue delays and within 24 hours after completion of the layer. Drying out of the layer must not be allowed. The curing membrane shall be applied at a spray rate that gives minimum 0.5 l/m2_{of residual bitumen.}

Bitumen emulsion is the preferred type of bituminous curing membrane. However cutback bitumen, MC30 or MC70 prime, may be used if trials show no adverse effect such as loosening of the surface of the layer. Traffic shall be kept off the completed layer for minimum 7 days after completed compaction. The curing membrane shall be protected from damage by traffic. Sanding-off after the curing period shall be employed if required due to site conditions.

Curing method - cemented subbase

Granular base course material shall be placed on the cemented subbase in a loose thickness of minimum 50 mm - and watered - without undue delays and within 48 hours after completion of the cemented layer. Drying out of the layer must not be allowed. Alternatively a temporary granular layer of minimum 50 mm loose thickness can similarly be spread and watered, and removed immediately before placing the base course.

The cemented subbase shall receive a bituminous curing membrane in the cases where a bituminous base course is used. The applied method shall be as described for curing of cemented base courses.

s s a l c l a i r e t a m d n a r e s il i b a t Stabiilserandmaterialclass Stabiilserandmaterialclass Stabiilserandmaterialclass Stabiilserandmaterialclass S AAAAAllllllllllooooowwwwweeeeeddddd itititititmmmmmeeeeefffffooooorrrrrcccccooooommmmmpppppllllleeeeeitititititooooonnnnn M C , 1 C , 2 C , 4 C -t n e m e C max4hours 1 C , 2 C , 4 C -e m i L max8hours M C -e m i L max48hours e m il h ti w n o it c a e r d i p a r e r o m a e s u a c y a m s e t e r c l a c n i e t a n o b r a c m u i c l a c f o s t n e t n o c h g i H s a d e r e tl a e b ll a h s n o it e l p m o c r o f e m it d e w o ll a m u m i x a m e h t s e s a c h c u s n I . d e t c e p x e n a h t . e ti s n o s l a ir t r e tf a d e ri u q e r

It is recommended practice to mix in water to at least OMC of BS-Heavy before adding the stabiliser, thereby minimising the required time for watering and mixing after the stabiliser has come in contact with the material.

Curing by continuous watering is likely to cause leaching out of stabilisers in the surface, there is a risk of detrimental wetting/drying cycles to take place and the method is overall unlikely to be effective in practice.

Penetration of bituminous prime into fresh cemented materials is not desirable as this can cause impaired conditions for curing of the upper part of the layer.

curing membrane

cemented base course

Loose 50 mm -granular layer to be kept wet.

(9)

Chapter 7 Pavement Materials

Comments:

7.3.6 Other chemical stabilisers

Chemical stabilisers other than bitumen, cement or lime, may only be used on agreement with the Ministry of Works at project level. Such alternative stabilisers include ionic soil stabilisers and other chemical products sold under various brand names.

The following issues shall be clarified for each project before use of alternative chemical stabilisers are allowed in structural layers:

n certification of the chemicals effect on personnel and environment

n required properties of the stabilised material to suit the requirements of the structural layer in question

n required properties of the source materials and their availability

n mix formula

n routines for laboratory testing and quality assurance

n assessments of material properties over time

n contractual obligations of suppliers

n the possibility for competitive bidding

7.4 Bituminous Base Course

Materials

7.4.0 General

Scope

This chapter includes bitumen penetrated macadam and bituminous mixes used in the base course - whether mixed in plant or mixed on the road. The appropriate use of each individual material type, such as limitations with regards to traffic, is set out in the pavement design catalogue

/Chapter 8.3.2/.

Alternative bituminous base course materials that are not included here, shall have their properties measured against the requirements for the material types described in this chapter prior to approval for use.

Structural function of bituminous mixes for base course

Bituminous mixes for base course function as main structural layers and the desired properties are therefore primarily high stiffness and resistance against deformation. The ability of the bituminous mix to withstand plastic deformation is emphasised due to the severe consequences with costly repair of such type of distress. The method to minimise the risk of fatigue cracking is primarily by providing the stiffest possible support and thereby minimising strain in the base course layer.

The largest possible aggregate size corresponding to the layer thickness is desirable for economical reasons and to provide high shear strength in the layer.

Description and structural function of penetration macadam

Construction of penetration macadam involves spraying of relatively large amounts of bitumen on a layer of coarse aggregate without fines, and subsequently rolling in a layer of chipping as a key stone to provide interlocking and stability of the layer. Alternatively a bituminous mix can be used instead of key stone. The function of the penetration macadam is fundamentally different from the bituminous mixes - being exceptionally

Alternative chemical constituents including ionic soil stabilisers and various products from the chemical industry have been used in soil stabilisation in some countries and there are reports on successful use under given conditions. These stabilisers should be reserved for trials unless the long-term stabilising effect of the particular product is properly documented.

There is a considerable amount of innovative work being done in the field of bituminous materials and this manual cannot fully include specialised material types which may be proposed for projects.

It is considered risky to compromise resistance against deformation of the bituminous base course for high res-istance against fatigue cracking under the prevailing temperature conditions.

Penetration macadam base course has been used successfully in this country on a large scale giving excellent service life. The high flexibility allows penetration macadam to be used successfully in pavements with marginal stiffness in supporting layers, such as on lightly

(10)

Chapter 7 Pavement Materials

Comments: flexible and able to absorb deficiencies in the strength of sub-layers, and

at the same time providing high shear strength. Penetration macadam is particularly well suited on roads with low traffic speed such as urban roads. On roads with high traffic speed a levelling layer of a bituminous mix will provide the required riding quality.

7.4.1 Classification

Classes of bituminous base course materials are shown in Table 7.10.

Table 7.10 Bituminous base course - material classes

7.4.2 Hot bituminous mixes

Dense Bitumen Macadam (DBM)

Dense bitumen macadam for base course layers shall comply with the requirements in Table 7.11.

Table 7.11 Material requirements DBM

Material

properties

DBM 40

DBM 30

CML test method

Dense bitumen macadam Dense bitumen macadam

Max nominal size 40 mm 30 mm

Grading, sieve

sizes [mm] % passing % passing

50 100 37.5 95 - 100 100 28 70 - 95 90 - 100 20 - 70 - 95 14 56 - 76 58 - 82 10 53 - 70 52 - 73 5 39 - 56 40 - 56 1.7 2 24 - 40 24 - 40 1,18 19 - 35 19 - 35 0,425 9 - 25 9 - 25 0,300 7 - 21 7 - 21 0,075 2 - 9 2 - 9 3.22 Type of bitumen Aggregate strength Layer thickness 80 - 200 mm 60 - 150 mm Bitumen content nominally 4.0% nominally 4.5%

60/70 or 40/50 penetration grade

Material class

TFVsoaked : min 75% of TFVdry

TFVdry: min 110 kN 2.7 s s a l c l a ir e t a Mate iralclass Mate iralclass Mate iralclass MMate iralclass CCCCChhhhhaaaaarrrrraaaaacccccttttteeeee iririririrsssssitititititcccccsssss e m a N Process Mi ixngmethod M B D _mDe_an_cs_ae_d_ab_mtiumen Hot ,t n a l p g n ix i M S B M A L L_f_oa_rrg_be_a_sa_eg_sgregatemix Hot M P _mPe_an_ce_a_drta_a_miton Cold Ontheroad,sprayed, X I M B F Foamedbtiumenmix Cold e h t n o r o t n a l p g n ix i M , d a o r X I M E B Btiumenemulsionmix Cold trafficked roads. Penetration macadam

can be constructed by the use of labour intensive methods and is well suited for construction in areas with restricted access by heavy plant and where it is difficult to perform good layer-work techniques which are often critical with alternative material types.

Chapter 7.4.2

Chapter 7.4.3

Chapter 7.4.4

(11)

Chapter 7 Pavement Materials

Comments: Large Aggregate Mix for Base Course (LAMBS)

LAMBS is a hot mixed bituminous material for base course on heavily trafficked roads and areas of extreme loading, such as climbing lanes. Large Aggregate Mixes (LAMBS) obtain their strength and resistance to deformation primarily from aggregate interlock and exhibit the following typical features:

n large upper nominal particle size (d_MAX up to 50 mm) and flexibility in grading requirements, giving good crushing economy

n high stability and shear strength, providing good resistance against deformation caused by heavy loading

n low required bitumen contents for good economy

LAMBS shall comply with the requirements in Table 7.12. The design met-hod for LAMBS shall be carried out in accordance with /7 - 5/. The design method for LAMBS requires special equipment for preparation of test specimens due to the large aggregate size. If such equipment is not available the material type DBM 40 shall be the alternative for the base course.

Table 7.12 Material requirements - LAMBS

*) _{The target grading curve is derived from the formula given below. The shape of the}

grading curve shall be such that it falls within the outer limits defined by an n value from 0.4 to 0.7 as specified in Table 7.12. The formulae for the n value is the following:

(100 - F) ( dn_0.075n₎

P = + F (Dn_{- 0.075}n₎

where:

P = percentage passing sieve size d (mm) D = max particle size ( dMAX )

F = filler content

n = a parameter to describe the shape of the grading curve

The aim in the design of LAMBS is to optimise the properties of available materials and plant and grading envelopes are therefore not specified.

Material

LAMBS

CML test

properties Large aggregate mix for base course method

Aggregates shall be made by crushing of fresh rock or clean, large boulders with a diametre >0.3 m. min 37.5

max 50 Shape of the grading min 0.4 *)

curve, n-value max 0.7

Aggregate TFVsoaked 24hrs : min 75% of TFVdry

strength TFVdry: min 110 kN

Aggregate LS [%] max 2 1.4

Filler content, pass. 0.075 mm [%] 5 - 8 1.7

Traffic TLC 20 and TLC 50: 40/50 pen. grade Traffic TLC 1 to TLC 10: 60/70 pen. grade

Bitumen content [%] 3.5 to 4.5 to be determined in the mix design 3.22 Mix design Shall be carried out in accordance with Ref/7- 4/

min 1.5 x ( dMAX ), preferably 2 x ( dMAX )

80 - 200 mm compacted thickness 3.5 Aggregate type Bitumen grade Layer thickness 2.7 Max particle size, dMAX [mm]

1.7

Water absorption [%] max 3 3.13

Values of n higher than 0.7 may result in segregation and poor workability.

(12)

Chapter 7 Pavement Materials

Comments:

7.4.3 Penetration macadam

Penetration macadam base course materials shall comply with the requirements in Table 7.13.

Table 7.13 Material requirements penetration macadam

A bituminous mix can be used instead of key stone to provide stability in the penetration macadam. The bituminous mix shall meet the

requirements in Chapter 7.4.2 or /Chapter 10.8/ in the case of hot mixed material and Chapter 7.4.4 for cold mixed material. The upper nominal aggregate size of the bituminous mix shall be adjusted as required to provide sufficient interlocking with the macadam layer. The bitumen spray rates for penetration, as given in Table 7.13, can be reduced in the case a bituminous mix is used instead of key stone. Site trials shall be undertaken to prove that the proposed reduction is possible without causing instability of the layer.

7.4.4 Cold bituminous mixes

General

Cold bituminous mixes have the advantage that they can be mixed on the road because they need no heating, thus making it possible to reuse and improve existing layers in place by in-situ milling. In order to enable mixing and coating of aggregate particles in cold bituminous mixes it is necessary to use bitumen that is either:

Material CML

test method

properties _{PM 80} _{PM 60} _{PM 30}

Max nominal size [mm] 80 60 30

125 100 50

The layer thickness of the penetration macadam should correspond with the aggregate fraction in order to obtain stability of the layer.

Bitumen spray rate [l/m2] *) 3 - 4 3 - 4 2 - 3

3.5

Bitumen type 80/100 or 60/70 penetration grade

Aggregate strength TFVsoaked : min 75% of TFVdry TFVdry: min 110 kN 2.7

Grading, sieve Main fraction

sizes [mm] _{% passing} _{% passing} _{% passing}

100 100 - -75 75 - 100 100 -63 - 80 - 100 -50 0 - 50 0 - 50 -37,5 0 - 25 0 - 25 100 2.3 28 0 - 5 0 - 5 80 - 100 20 - - 0 - 50 14 - - 0 - 25 10 0 - 5 Flakiness Index - - 35

Grading, sieve Key stone *)

sizes [mm] % passing % passing % passing

50 100 - -37,5 85 - 100 100 -28 0 - 50 85 - 100 -20 0 - 25 0 - 50 100 14 0 - 5 0 - 25 85 - 100 2.3 10 - 0 - 5 0 - 55 6.3 - - 0 - 25 5 - - 0 - 10 Flakiness Index - 35 35 Material class Layer thickness [mm]

*) Requirements for alternative use of a bituminous mix instead of key stone are set out in the text.

2.4

Penetration macadam made by use of a bituminous mix instead of key stone gives the following advantages:

- improved riding quality

- a better surface texture for subsequent application of a surface treatment, whereby full waterproofing of the surface is more easily achieved Comments:

(13)

Chapter 7 Pavement Materials

Comments:

n emulsified to reduce viscosity at the time of mixing, or

n foamed in order to greatly expand its volume and thereby facilitate coating of the particles

This chapter sets out requirements for cold mixes where foamed bitumen or bitumen emulsion is used. Cutback bitumen shall not be used in mixes due to potential stability problems during curing and for environmental reasons associated with the use of large amounts of solvents.

Foamed bitumen mix FBMIX

Foaming of bitumen is temporary expansion of the bitumen to 15-20 times its original volume by controlled introduction of small amounts of water in hot bitumen, carried out in a special processing plant. Foamed bitumen shall meet the requirements in Table 7.14.

Table 7.14 Requirements for foamed bitumen

Cold bituminous mixes for base course, made with foamed bitumen, shall comply with the requirements in Table 7.15. Aggregate for foamed bitumen mixes can be natural gravel or crushed materials. The required moisture content in the mix is determined in the mix design and shall be within the limits given in Table 7.15 at the time of laying.

Due to the alternative use of natural gravel aggregates in cold mixes the density of the mix may vary considerably thus rendering conventional expression of bitumen content as a percentage by weight misleading, unless accompanied by the density of the actual mix.

Plastic aggregates may give operational problems during mixing and laying even if the requirement of PI max 14% is fulfilled.

/Appendix A1- Definitions of Terms/ includes the definition of dry density of mixes where both bitumen and water is present. n e m u ti b d e m a o f e h t f o s e it r e p o r Properitesofthefoamedbtiumen Properitesofthefoamedbtiumen Properitesofthefoamedbtiumen PProperitesofthefoamedbtiumen RRRRReeeeeqqqqquuuuuriririririeeeeemmmmmeeeeennnnntttttsssss e t a t s d e m a o f a n i n e m u ti b f o e m u l o v n e e w t e b o it a R e t a t s d e m a o f-n u n a n i d n a min15 e b ll a h s s t n e m e ri u q e r g n i w o ll o f e h t f o e n o t s a e l t A : d e ll if l u f d e s a e r c e d s a h m a o f e h t f o e m u l o v e h t li t n u e m i T . 1 e m u l o v m u m i x a m s ti f o fl a h o t d e m a o f a n i n e m u ti b f o e m u l o v n e e w t e b o it a R . 2 s d n o c e s 5 1 r e tf a e t a t s d e m a o f-n u n a n i d n a e t a t s 5 1 n i m s d n o c e s 5 . 7 n i m .t e k c u b l a c ir d n il y c e rt il 0 1 a s e s il it u n e m u ti b d e m a o f f o t s e t e h T

(14)

Chapter 7 Pavement Materials

Comments: Table 7.15 Material requirements FBMIX

Bitumen emulsion mix - BEMIX

Cold mixed bitumen emulsion for stabilisation of base course layers with minimum 3.5% residual bitumen content shall comply with the

requirements in Table 7.16. Materials with smaller amounts of binder shall be classified as bitumen modified and the design of such materials shall be carried out in accordance with /7 - 10/.

7.4.5 Construction

Penetration macadam

Penetration macadam base course normally requires no special preparat-ion of the underlying surface. Compactpreparat-ion shall be carried out with vibrating rollers and the number of passes shall be min 3 max 5. The number of passes after application of keystone shall be min 2 max 4.

Hot mixes

Tack coat of bitumen emulsion shall be applied at a rate giving minimum 0.3 l/m2_{residual binder on all joints and surfaces where hot mixed} bituminous base course is laid. The required minimum temperature for compaction shall be in accordance with /Chapter 10.8.4/.

Material Material class

properties FBMIX CML test

Foamed bitumen mix method

Aggregate source Natural gravel or crushed material, free from lumps of clay or other deleterious matter.

PI [%] 1) max 14 before admixture of bitumen 1.2 and 1.3

CBRsoaked [%] min 30 before admixture of bitumen, tested at 95 % MDD of BS-heavy 1.11

Aggregate TFVsoaked : min 75% of TFVdry

strength Traffic TLC 3 and TLC 10: TFVdry: min 110 kN

Traffic TLC 1 and lower: TFVdry: min 80 kN

Grading, sieve sizes [mm] % passing 37,5 100 28 80 - 100 20 60 - 95 10 42 - 78 5 30 - 65 2 20 - 50 0,425 10 - 30 0,075 5 - 15

E-Modulus [MPa] min 1600, measured by indirect tensile strength, tested at 29oC 3.21

Marshall stability [N] min 6000 tested at 40oC Marshall flow [mm] 2 - 4

Moisture content at min: mix design moisture less 1.5% points the time of laying [%] max: mix design moisture plus 0.5% points

Type of bitumen 80/100 or 150/200 penetration grade 3.5

Adhesion agents Approved adhesion agents shall be admixed at min 0.5% by weight of bitumen

Bitumen content Consumption, residual bitumen: 80 to 100 litres per m3 of compacted material 3.22 Field density min 96% of Marshall dry density

1.1 2.7

1.7

3.18

When bitumen emulsion is used, as opposed to foamed bitumen, the material is more sensitive to aggregate properties such as grading, plasticity index and fines content and correct moisture content, and is also more prone to damage by rain. In many cases the adding of a cement slurry with 1 - 2% cement may be beneficial.

(15)

Chapter 7 Pavement Materials

Comments:

Material Material class CML test

properties BEMIX method

Bitumen emulsion mix

Aggregate source Natural gravel or crushed material, free from lumps of clay or other deleterious matter.

PI [%] 1) max 8 before admixture of bitumen 1.2 and 1.3 CBRsoaked [%] min 30 before admixture of bitumen, tested at 95 % MDD of BS-heavy 1.11

Aggregate TFVsoaked : min 75% of TFVdry

strength Traffic TLC 3: TFVdry: min 110 kN

Traffic TLC 1 and lower: TFVdry: min 80 kN

Grading, sieve sizes [mm] % passing 37,5 100 28 80 - 100 20 60 - 95 10 35 - 70 5 25 - 50 2 18 - 35 0,425 10 - 25 0,075 5 - 8

E-Modulus [MPa] min 1200, measured by indirect tensile strength, tested at 29oC 3.21 Marshall stability [N] min 4500 tested at 40oC

Marshall flow [mm] 2 - 4

Moisture content at min: mix design moisture less 1.5% points the time of laying [%] max: mix design moisture plus 0.5% points

Type of base bitumen 80/100 or 150/200 penetration grade 3.5

Bitumen content Consumption, residual bitumen: 80 to 100 litres per m3 of compacted material 3.22 Field density min 96% of Marshall dry density

1.1 2.7

1.7

3.18

Table 7.16 Material requirements - BEMIX

Cold mixes

Tack coat of bitumen emulsion shall be applied at a rate giving minimum 0.3 l/m2_{residual binder on all joints and on surfaces towards other} bituminous layers and between adjacent layers placed in succession where the same type of material is used. Priming or application of tack coat shall be carried out as required if problems with slippage of the bituminous base course occur.

Compaction trials

Detailed compaction trials shall be carried out at the beginning of laying operations and when a new mix formula or production

procedure is introduced. The compaction trial shall show compliance with mix formulas and demonstrate the adequacy of the proposed compaction procedures. The compaction trial shall also confirm that equipment and procedures are adequate for paving at the proposed layer thickness while achieving satisfactory riding quality and sufficient density to the bottom of the layer.

Subbase made of cemented materials will have a bituminous curing membrane and may not require any further application of tack coat. Subbase made of natural gravel can normally receive a bituminous cold mix without use of prime. Comments:

(16)

Chapter 7 Pavement Materials

Comments:

7.5 Deleterious Minerals

Sulphide minerals

The maximum allowed /7 -21/ content of sulphide minerals such as pyrite, marcasite, and chalcopyrite, in aggregates are given in Table 7.17.

Table 7.17 Sulphide minerals in aggregates

Mica

Muscovite mica (light colour) causes difficulties in achieving compaction of granular layers and the initial density may decrease in service and promote ingress of water. Biotite mica (black colour) tends to break rather than behave like flexing plates in the soil matrix and is therefore of less concern. Contents of muscovite mica above 10% by volume are not allowed in granular pavement layers. No specific limit is set for biotite mica.

Soluble salts

Testing of electric conductivity is the preferred, simple, method to indirectly determine the content of soluble salts in soils and construction water. Special methods for design and construction of pavements with presence of soluble salts, including the setting of appropriate design limits, are discussed in /7-11/.

Rapidly weathering minerals

Rapidly weathering minerals, e.g. nepheline, or rock types such as some basic igneous rocks, require special testing to identify their potential for rapid weathering and to verify sufficient durability for use in pavement layers.

7.6Surveys for Construction

Materials

7.6.1 Borrow pits

Potential borrow pits shall be surveyed by trial pit excavations and sampling at the stage of detailed design. The survey shall prove sufficient quantities for all pavement and earthworks materials. The sampling frequency shall be minimum that given in Table 7.18.

e s u d e d n e t n Intendeduse Intendeduse Intendeduse Intendeduse I MMMMMaaaaaxxxxxcccccooooonnnnnttttteeeeennnnntttttooooofffff_[sssss_%uuuuu_]lllllppppphhhhhiiiiidddddeeeeemmmmmiiiiinnnnneeeeerrrrraaaaalllllsssss s l a ir e t a m s u o n i m u ti B max2 e s a b r o f s l a ir e t a m r a l u n a r G e s a b b u s r o e s r u o c max1 d e s il i b a t s e m il r o t n e m e C s l a ir e t a m Zeroallowed

The effect of mica is particularly adverse when the mica plates are larger than 0.5 mm diameter. A content higher than 10% by volume means that the mica is easily detectable at a glance during visual inspection.

/Chapter 6 Problem Soils/.

Testing to identify rapidly weathering minerals: /7-3/ and /7-9/.

(17)

Chapter 7 Pavement Materials

Comments: Table 7.18 Borrow pits - minimum test frequency prior to opening

7.6.2 Quarries

All new quarry sites of massive rock shall at the design stage be invest-igated by core drilling to establish sufficient quantities for the project. The extent of investigations shall be determined depending on site conditions and the type of project.

7.7 Manufactured Materials

7.7.1 Geo-textiles used as separating layers

General

Geo-textiles are used for separation of materials of different grading where there is a risk of undesirable infiltration of fines into the matrix of a coarser material.

Manufacture

The basic type of geo-textile shall be non-woven, manufactured by needle punching, thermal bonding, or both. The fibres shall be continuous or staple fibres made of either polyester or polypropylene.

Material requirements

Table 7.19 shows the minimum weight per m2_{for geo-textiles depending} on the site conditions.

e s u d e d n e t n Intendeduse Intendeduse Intendeduse Intendeduse I m x a Maxm Maxm Maxm MMaxm33333_t_t_t_t_t_o_o_o_o_o_b_b_b_b_b_e_e_e_e_e_r_r_r_r_r_e_e_e_e_e_p_p_p_p_p_r_r_r_r_r_e_e_e_e_e_s_s_s_s_s_e_e_e_e_e_n_n_n_n_n_t_t_t_t_t_e_e_e_e_e_d_d_d_d_d_b_b_b_b_b_y_y_y_y_y_o_o_o_o_o_n_n_n_n_n_e_e_e_e_e_t_t_t_t_t_e_e_e_e_e_s_s_s_s_s_t_t_t_t_t R B C G_ar_na_ddi_Png_I A_sgg_rt_ere_n_gg_ta_hte e s r u o c e s a b s u o n i m u ti B 5000 3000 10000 e s r u o c e s a b d e t n e m e C 5000 5000 20000 e s a b b u s d e t n e m e C 10000 10000 -l e v a r g .t a n -e s r u o c e s a B 5000 3000 20000 l e v a r g l a r u t a n -e s a b b u S 10000 5000 e d a r g b u s d e v o r p m I 10000 10000 ll i F 20000 20000 -.t i p w o r r o b h c a e n i d e t a v a c x e e b ll a h s s ti p l a ir t r u o f n a h t s s e l o N

Existing quarries may be investigated by proof drilling, core drilling, trial blasting or as required depending on site conditions such as the size of current operations compared to required future operations for the project.

Geo-textile used for prevention of reflective cracking in pavement rehabilitation works is discussed in Chapter 9.4. Other possible uses of geo-textiles, such as in drainage works, are not included in this manual.

Both cost and quality of geo-textiles are in general proportional to their weight per m2_{, and the required quality depends on}

the maximum particle shape, particle size and compression strength of the material to be placed against the geo-textiles.

(18)

Chapter 7 Pavement Materials

Comments: Table 7.19 Geo-textile separating layers required weight per m2

Storage

Geo-textiles shall be kept away from direct sunlight during storage.

7.7.2 Geo-grids for reinforcement

General

Geo-grids are intended for use as reinforcement of earthworks and pave-ment layers. Geo-grids shall only be considered in special cases due to their high cost. The technical and economical effectiveness of their use shall be carefully assessed and documented before application in the works.

Earthworks

Geo-grids may be considered in special cases such as to prevent tensile failure at the bottom of embankments when crossing soft areas.

Pavements

Geo-grids do not add strength to the pavement structure to an extent that make them economically justified in new pavements. No reductions in pavement layer thickness shall be made due to the use of geo-grids. Geo-grids may be considered under special circumstances for use in an interlayer system to prevent reflective cracking through overlays.

References

7 - 1 AMERICAN SOCIETY FOR TESTING AND MATERIALS (1987).

Annual Book of ASTM Standards, Vol. 4.08. Philadelphia, USA.

7 - 2 AUSTRALIAN ASPHALT PAVEMENT ASSOCIATION (1997). Cold

Mix Granular Materials Guide.

7 - 3 HOSKING, J R and TUBEY, L W (1969). Research on low-grade and

unsound aggregates. RRL Report LR 293. Transport research

laboratory, Crowthorne, London, UK.

7 - 4 NETTERBERG, F (1985). Pedocretes. From Engineering Geology of Southers Africa. NITRR report 430 Pretoria, Republic of South Africa.

t n e c a j d a d e c a l p e t a g e r g g Aggregateplacedadjacent Aggregateplacedadjacent Aggregateplacedadjacent AAggregateplacedadjacent e li t x e t-o e g e h t o t GGGGGeeeeeooooot-t-t-t-t-eeeeexxxxxtttttlililililieeeee,,,,,wwwwweeeeeiiiiiggggghhhhhtttttpppppeeeeerrrrraaaaarrrrreeeeeaaaaa[[[[[ggggg/////mmmmm 22222_]]]]] e p y t e t a g e r g g A dMAX ] m m [ , m ri f n o d e c a l P li o s b u s y r d 1) _wP_ela_tc_se_ud_bo_s_on_lisof2),t r o d n a s ,l e v a r G d e h s u r c d e d a r g l a ir e t a m max50 min140 min200 d e h s u r c d e tr o S k c o r max200 min200 min320 k c o r p m u D ) R D ( - min320 l a i c e p S ll a h s t n e m e c r o f n i e r d e r e d i s n o c e b .t h g i L -S B f o C M O w o l e b s t n e t n o c e r u t s i o m o t s r e f e r li o s b u s y r D ) 1 . s a e r a d e g g o l r e t a w n i s l a ir e t a m y e y a l c r o y tl i s y ll a m r o n s i li o s b u s t e w ,t f o S ) 2

Geo-textiles made of polypropylene are particularly sensitive to the effect of direct sunlight.

Geo-grids within the embankment itself have doubtful effect and should only be considered when used in specially designed systems of earth reinforcement for construction of steep slopes.

Use of geo-grids to prevent reflective cracking in pavement rehabilitation works is discussed in /Chapter 9.4/.

(19)

Chapter 7 Pavement Materials

Comments:

7 - 5 NETTERBERG, F and M I PINARD (1991). Derivation of interim

performance-related specifications for coarsely-graded plastic calcrete basecourse gravels. Proc. 10th Regional Conference for Africa on Soil

Mechanics and Foundation Engineering, Maseru, Leshoto.

7 - 6 SOUTHERN AFRICAN BITUMEN ASSOCIATION - SABITA (1993).

LAMBS The design and use of large aggregate mixes for bases. Republic of South Africa.

7 - 7 TRANSPORT RESEARCH LABORATORY (1993). A guide to the

structural design of bitumen-surfaced roads in tropical and sub-tropical countries. Overseas Road Note No. 31. TRL, Crowthorne, for

ODA, London, UK.

7 - 8 CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION

ASSOCIATION (1988). Laterite in road Pavements. Special Publication 47. CIRIA, London, UK.

7 - 9 COMMITTEE OF STATE ROAD AUTHORITIES. Draft TRH 13

(1986): Cementitious stabilisers in road construction. CSRA, Pretoria, Republic of South Africa.

7 - 10 SOUTHERN AFRICAN BITUMEN ASSOCIATION - SABITA (1993).

Draft guidelines on the use of bitumen emulsion treated materials.

Republic of South Africa.

7 - 11 OBIKA, B and R J FREER-HEWISH (1990). Soluble salt damage to

thin Bituminous surfacings of roads and runways. Australian Road

Research, 20 (4.)

7 - 12 BOTSWANA ROAD DESIGN MANUAL (1994). Draft Volume 3,

Materials and Pavement Design. Ministry of Works, Transport and

Communications, Roads Department. Republic of Botswana.

7 - 13 COMMITTEE OF STATE ROAD AUTHORITIES. TMH 5 (1981):

Sampling methods for road construction materials. CSRA, Pretoria,

Republic of South Africa.

7 - 14 COMMITTEE OF STATE ROAD AUTHORITIES. TRH 8 (1987):

Selection and design of hot-mix asphalt surfacings for highways.

CSRA, Pretoria, Republic of South Africa.

7 - 15 COMMITTEE OF STATE ROAD AUTHORITIES. TRH 14 (1985):

Guidelines for road construction materials. CSRA, Pretoria, Republic

of South Africa.

7 - 16 LIONJANGA, A V and T TOOLE and P A K GREENING (1987). The

use of calcrete in paved roads in Botswana. Ninth regional conference

for Africa, Lagos, Nigeria.

7 - 17 NATIONAL ASSOCIATION OF AUSTRALIAN STATE ROAD

AUTHORITIES (1986). Guide to stabilisation in roadworks. NAASRA, Sydney, Australia.

7 - 18 OCONNELL M J and C S GOURLEY (1993). Expansive clay road

embankments in arid areas: moisture-suction conditions. Proc. First

International Symposium on Engineering Characteristics of Arid Soils, City University. London, UK.

7 - 19 ROAD DESIGN MANUAL (1987). Part III, Materials and Pavement

Design for New Roads. Ministry of Transport and Comm., Roads

Department. Republic of Kenya.

7 - 20 TOOLE, T and D NEWILL (1987). A Strategy for assessing marginal

quality materials for use in bituminous roads in the tropics. Proc.

seminar H, PTRC Transport and Planning Summer Annual Meeting, University of Bath, London, UK.

7 - 21 WEINERT, H H (1980). The natural road construction materials of