Curb (kerbstone) vs pavement construction sequence and installation essentials: embedded curbs must be set before surface courses; curb bases preferably built with the road base

Topic Positioning

The sequence between curbs and pavement structural layers in road works (municipal roads, interlocking-block pavements, depot roads), plus curb installation controls (stake spacing, mortar bedding, backrest concrete, backfill compaction, jointing and curing) — for reviewing method statements and technical briefings on "when and how curbs are installed".

Core Conclusions

1. Sequence: curbs (and bases) first, surface courses after

1. GB 50092-96 "Code for construction and acceptance of asphalt pavement", 10.5.4: "Embedded curbs must be fully installed before asphalt surface construction. After embedding, backfill shall be compacted or protective measures taken against deformation during surface construction. Cutting the paved asphalt layers to bury curbs is strictly forbidden."
2. CJJ/T 303-2020 (medium-low speed maglev), 9.3.6(1): "Embedded curbs shall be installed before pavement structural layers; curbs shall not be laid by cutting the pavement afterward. After embedding, compact the backfill or protect against deformation."
3. CJJ 1-2008 "Code for construction and quality acceptance of urban roads", 16.1.5: "Curb bases should be built simultaneously with the corresponding base courses." DB11/T 1834-2021, 9.2.3 adds: "Cut trenches per the surveyed position and level, level and compact, then set curbs."
4. Interlocking-block pavements (CJJ 79-98, 6.3): curbs edge-restrain the pavement — "curbs shall be laid first, preventing loss of the sand bedding and better restraining the pavement edge, ensuring interlock and arch action of the blocks".
5. Recommended flow: survey/trench -> curb base (with the base course) -> set curbs on mortar, joint -> pour backrest concrete, compact backfill -> pave surface. Re-trenching a finished surface to embed curbs is expressly forbidden.

2. Installation controls (CJJ/T 303-2020, 9.3.6)

• Control stakes: 10-15m on straights; 5-10m on curves; 1-5m at intersections.
• Set curbs on dry-hard mortar, full and even; stable, straight on tangents, smooth on curves, even joints; joints densely filled; flush curbs smooth and non-ponding.
• Backrest: cast concrete support behind curbs and compact backfill; width >= 500mm, height >= 150mm, compaction >= 90%.
• Joint with M10 mortar; cure >= 3d at normal temperature.
• Materials and documents: precast blocks, stone, or brick curbs shall meet strength requirements; preferably factory-made with strength/size certificates; curved sections prefabricated to design radii or with small standard blocks.

3. Supplementary construction/QC (T/AACPM 002-2020, 10.1.2)

• Trial sections required to fix parameters before full-scale work.
• Backrests preferably cast C15 concrete, formed per drawings, not widened to reduce height; backfill promptly after casting, >= 50cm wide, >= 15cm high.
• Green-belt heads and intersection radii: curved pieces per radius — no cutting straight curbs.
• QC: strength per type per lot, 1 group (3 pieces), factory reports; stability, mortar fullness, exposed-face cleanliness, smooth lines — full visual inspection; setting tolerances per its Table 10.1.2.

Applicable Boundaries

• Distinguish mandatory vs recommended: "must/strictly forbidden/shall not" (embedded curbs before surface; no cutting after paving) are mandatory; "should" (base simultaneity, backrest form) is recommended — design governs where specified.
• "Curbs first" applies to embedded curbs vs asphalt/structural layers; interlocking-block pavements stress curbs first to protect the sand bedding. Non-embedded flush-stone practices follow their design and codes.
• Backrest dimensions (>= 500mm wide, >= 150mm high, >= 90% compaction), C15 backrest, M10 jointing are code values or typical practice — design drawings and contracted standard editions govern; where local and industry standards coexist, follow the contract.
• This card does not cover curb norm item selection or pricing (see the related pricing card).

Further Reading

• GB 50092-96, 10.5.4 (sequence, incl. the prohibition).
• CJJ 1-2008, 16.1.5.
• CJJ/T 303-2020, 9.3.6 (full 8-clause curb provisions).
• CJJ 79-98, Section 6.3 (interlocking-block curbs first).
• DB11/T 1834-2021, 9.2.3.
• T/AACPM 002-2020, 10.1.2 (process, backrest, backfill, QC tolerances).
• Verify current editions and local clauses before use.